The Ultimate Guide to Mop Sinks Commercial

A commercial mop sink is the low, deep stainless steel basin every restaurant, bar, food truck commissary, and institutional kitchen is required to install for filling mop buckets and disposing of dirty floor-cleaning water. The FDA Food Code, the Uniform Plumbing Code, and the International Plumbing Code all require one - and the single biggest reason restaurants fail their plumbing inspection is getting the mop sink wrong. Wrong faucet height, missing vacuum breaker, undersized drain, or worse - no service sink at all and a wash sink getting used for mop water.

This guide walks through everything you need to spec, buy, install, and maintain a code-compliant mop sink in 2026: sizing and dimensions, faucet height rules, rough-in plumbing, NSF and ETL certification, the Atosa MRS-1-MOP deep spec review, daily and weekly maintenance, and 27 of the most-asked questions inspectors and operators ask. By the end you will know exactly which mop sink fits your closet, what to budget, and how to pass inspection on the first try.

Skip ahead - shop the gear: Atosa MRS-1 Mop Sink ($589) · All Commercial Sinks · 3-Compartment Sinks · Hand Sinks · ATDM Drain Maintainer

Key Takeaways

• A commercial mop sink (also called a service sink, mop basin, or janitor sink) is the only code-approved fixture for filling and dumping mop water in a food-service facility. The FDA Food Code and most state health departments treat it as mandatory wherever mops are used.
• Standard floor-mount basin sizes are 24x24, 24x36, and 36x36 inches. Most kitchens fit 24x24 or 24x36 because they tuck into a closet without eating walk-aisle space.
• Faucet spout height must clear the flood rim of the basin by at least one inch with a vacuum breaker installed above the highest possible water level - usually 6 to 8 inches above the rim. This is the most-cited plumbing-code violation on mop sinks.
• The Atosa MRS-1 18-gauge stainless mop sink ($589) is our top pick for restaurants under 3,000 square feet. It ships free, meets NSF, and slots into a 30-inch janitor closet.
• For bigger operations or multi-station setups, pair the mop sink with a separate three-compartment sink for warewashing and a dedicated hand sink for staff handwashing - never cross-use them.

What Is a Commercial Mop Sink (and Why Code Requires One)

A commercial mop sink - also called a service sink, mop basin, janitor sink, or janitorial sink - is a low, deep basin built specifically for filling mop buckets and disposing of dirty cleaning water. It sits on the floor or low on the wall, has a high faucet spout to clear bucket rims, and drains to a sanitary sewer line just like any other plumbing fixture in your kitchen.

The reason it gets its own dedicated fixture comes down to cross-contamination. Dirty mop water carries food soils, fats, grease, detergents, and bacteria. If that water hits a handwashing sink, prep sink, or warewashing sink, you have created a vehicle for foodborne illness - and a guaranteed inspection citation.

Why a Mop Sink Is Required by Code

The 2022 FDA Food Code §5-203.13 states that a service sink or curbed cleaning facility must be provided in every food establishment for the cleaning of mops, similar wet-floor equipment, and for the disposal of mop water and similar liquid waste. The exact language used in inspections is: "a janitor's sink is required."

State and local plumbing codes layer on top of that. The Uniform Plumbing Code (UPC §418.0) and the International Plumbing Code (IPC §418) both require a separate service sink with a vacuum breaker. Most municipalities also require a floor drain in the mop closet so any overflow can escape without flooding the kitchen.

If your inspector cannot find one of these three things - a dedicated service sink, a vacuum breaker on the faucet, and a code-compliant drain - you will fail. We have seen brand-new buildouts shut down on opening day for missing a $42 vacuum breaker.

Mop Sink vs. Floor Sink vs. Utility Sink - Don't Confuse Them

These three fixtures look similar in catalogs but serve completely different jobs:

• Mop sink (service sink): Has a raised wall on three sides, a curb to keep water in, and a faucet 24+ inches above the floor with a vacuum breaker. Used for filling mop buckets and dumping cleaning water.
• Floor sink: A flush-mounted indirect waste receptacle, usually 12x12 inches, that sits in the floor and receives drain lines from refrigeration equipment, ice machines, and steam tables via an air gap. You cannot fill a mop bucket from a floor sink - there is no faucet.
• Utility sink: A general-purpose deep sink (also called a laundry tub or slop sink) mounted on legs or a wall. Acceptable for janitorial use in some jurisdictions if it has a vacuum breaker, but most health departments now require a true mop sink for new construction.

If your contractor specs a "utility sink" in the plans, get clarification in writing that it meets local code as a service sink before installation. Repiping a janitor closet after the slab pour costs four figures.

How to Choose a Mop Sink: Material, Gauge, and Form Factor

Stainless Steel vs. Molded Stone vs. Fiberglass

You will see three materials when you shop:

• 304 stainless steel: The gold standard. Resists chlorine bleach, quaternary ammonium sanitizers, degreasers, drain cleaners, and physical impact. Lasts 15+ years even in punishing janitor-closet environments. Fully NSF-listed and welded seams stay watertight.
• 430 stainless steel: Cheaper magnetic stainless used on budget mop sinks. Resists most cleaners but will spot and pit under daily chlorine exposure. Acceptable for low-volume operations under 1,500 sq. ft.
• Molded stone (terrazzo, mop receptor): Concrete-and-marble composite floor receptor. Indestructible from impact, very heavy (250+ lbs), but the porous surface absorbs grease and odors over time. Common in schools and warehouses, less common in food service.
• Fiberglass / molded composite: One-piece molded basin, lightweight, chip-resistant. Decent middle ground for back-of-house but stains permanently if you leave bleach to sit.

For a commercial kitchen, we recommend 304 stainless every time. The labor cost of replacing a corroded fiberglass basin after three years exceeds the upfront savings.

16 Gauge vs. 18 Gauge Stainless

The number is the thickness of the steel sheet. Lower number means thicker steel:

• 16 gauge (1.5mm / 0.0598 inch): Heavy-duty. Used on premium mop sinks built for hotels, hospitals, and high-volume restaurants. Resists denting from dropped mop buckets and rolling carts.
• 18 gauge (1.2mm / 0.0478 inch): Standard commercial weight. Used on the Atosa MRS-1 and most mid-priced units. Plenty stiff for a restaurant under 5,000 sq. ft.
• 20 gauge (0.95mm): Light-duty. Found on residential utility tubs. Avoid for commercial use - basin will flex and seams may crack under repeated impact.

Floor-Mount vs. Wall-Mount vs. Corner

• Floor-mount basin: The most common form factor. Sits directly on the slab on its own integrated curb. No legs to corrode, easy to push a 35-quart bucket into. Drain exits through the bottom center or rear.
• Wall-mount mop sink: Hangs off the wall on a steel bracket. Better in tight spaces and easier to mop under. Drain runs out the bottom into a P-trap below.
• Corner mop sink: Triangular floor basin that tucks into a 90-degree wall corner. Saves about 30 percent footprint compared to a square unit. Best for converted closets in older buildings.

Drain Size and Rough-In

Mop sinks use a 3-inch drain almost universally, with a 3-inch P-trap and 2-inch vent. Smaller drains clog with mop strings and grit within months. The drain outlet on the Atosa MRS-1 is centered on the bottom rear and accepts a standard 3-inch threaded coupling.

Rough-in your hot and cold supply lines 28 to 32 inches above finished floor on the wall behind the basin. The vacuum breaker on the faucet sits 6 to 8 inches above the basin rim, so total faucet height ends up around 42 to 50 inches.

Mop Sink Dimensions: How to Pick the Right Size

Three sizes cover 95 percent of commercial installations:

Basin Size	Bucket Capacity	Best For	Closet Footprint Needed
24" x 24" x 10"	26-quart bucket	Small restaurants, coffee shops, food trucks with stationary location	30" x 30" minimum
24" x 36" x 10"	35-quart bucket + accessories	Mid-size restaurants, breweries, retail food	30" x 42" minimum
36" x 36" x 12"	Two 35-quart buckets side-by-side	Hotels, large kitchens, food production, schools	42" x 42" minimum

Pay attention to basin depth. A 10-inch-deep basin handles a full 35-quart mop bucket without splashing. A shallow 6-inch unit might fit the bucket but cannot fill or empty it without water arcing onto the wall and floor.

Always add at least 4 inches of clearance on each side of the basin for elbow room, plus 24 inches in front for the operator to stand and tilt a heavy bucket. A 24x24 basin needs a 32x48-inch closet minimum.

Atosa MRS-1-MOP Deep Spec Review (18 Gauge, NSF + ETL)

The Atosa MRS-1-MOP is our highest-volume mop sink and the most cost-effective NSF/ETL unit on the market for restaurants under 3,000 sq. ft. List price is $589 with free freight to commercial addresses in the lower 48. Here is the full technical breakdown.

Atosa MRS-1-MOP Complete Specifications

Feature	Specification
Model Number	MRS-1-MOP
Manufacturer	Atosa
Bowl Material	18-gauge stainless steel, one-sheet construction
Overall Dimensions	21"W x 21.5"D x 44.5"H
Bowl Dimensions	18"L x 18"D x 13"H (interior)
Leg Construction	Galvanized steel
Feet	Adjustable ABS bullet feet
Drain Board	Creased and angled toward drain outlet
Certifications	NSF certified, ETL listed (Intertek)
Faucet	Sold separately - sink unit only
Unit Price	$589.00
Freight Minimum	6 units for standard freight delivery (single units available via Will-Call pickup)

Why 18-Gauge One-Sheet Construction Matters

The MRS-1-MOP bowl is formed from a single sheet of 18-gauge stainless steel. In commercial kitchen equipment, gauge refers to thickness - lower gauge equals thicker steel. 18-gauge hits the sweet spot for mop sinks: heavy enough to resist dents from 35-quart buckets and rolling carts, light enough to keep the unit price under $600.

One-sheet construction is the critical detail. By forming the entire bowl from a single sheet, Atosa eliminates internal seams and welds inside the basin. Seams are the first place a utility sink fails - they harbor bacteria, harbor mineral buildup, and eventually corrode or leak under repeated chemical exposure. The smooth continuous interior surface of the MRS-1-MOP cleans in seconds with a quat sanitizer and a nylon brush.

Chemical Resistance and Daily Cleaner Compatibility

The 18-gauge stainless on the MRS-1-MOP resists pitting and corrosion from the chemicals you actually use in a janitor closet:

• Safe: Mild detergents, quat-based sanitizers, neutral floor cleaners, diluted chlorine bleach (rinse within 10 minutes)
• Safe with caution: Concentrated degreasers, alkaline floor strippers (rinse thoroughly after use)
• NEVER: Hydrochloric acid (muriatic acid), nitric acid, abrasive scouring powders, steel wool

The hydrochloric acid warning is the one that catches most operators off guard. Some heavy-duty drain openers and mineral-deposit removers are HCl-based. Even a few minutes of contact will pit 304 stainless and start a corrosion chain that voids any warranty. Stick with enzyme-based maintainers like ATDM Drain Maintainer for routine drain care.

Galvanized Legs and Adjustable ABS Feet

The MRS-1-MOP uses galvanized steel legs rather than full stainless. Galvanization coats the steel with zinc to resist rust at a fraction of the cost of stainless tube. The trade-off is that the legs need to stay dry - standing water under the unit will eventually eat through the zinc coating and start surface rust. Mount the sink with a 1/4-inch slope to the floor drain in the closet and the legs will outlast the bowl.

Adjustable ABS (Acrylonitrile Butadiene Styrene) bullet feet thread into the bottom of each leg. Restaurant slabs are rarely level - typical out-of-level on a 24-inch span is 1/8 to 3/8 inch. The feet adjust independently so you can shim the unit perfectly horizontal without stacking stainless washers. Level matters more than most operators realize: a sink tilted 1/4 inch toward the back leaves a half-inch of standing water in the front of the basin every time it drains. Standing water becomes a bacterial reservoir within 48 hours.

ABS feet are wear parts. Heavy use will eventually crack them - they are standard threaded inserts and replace in 30 seconds with a 7/16-inch wrench.

Creased and Angled Drain Board

The interior bottom surface is creased and angled toward the drain outlet. This is not cosmetic - it is the engineering detail that earns NSF certification. The creases act like miniature channels, directing water along defined paths toward the outlet rather than letting it pool in random low spots. The angle (roughly 1 to 2 degrees) provides gravity assist so the basin drains completely even after a slow-emptied bucket.

Sinks without this detail have what manufacturers call "dead zones" - flat areas where dirty water settles, dries, and grows biofilm. NSF specifically tests for dead zones during certification by filling a sink and measuring residual water 60 seconds after the strainer is pulled. The MRS-1-MOP passes that test.

NSF and ETL: What the Labels Actually Mean

• NSF Certification: The National Sanitation Foundation sets the design and construction standards for any equipment used in food service. NSF tests verify that the sink is built from non-toxic materials, has cleanable surfaces with no dead zones, sealed seams (or none at all), proper drainage, and corrosion-resistant fasteners. Every health inspector knows the NSF mark - missing it gets you written up.
• ETL Listed: ETL is a safety certification mark from Intertek, a global testing lab. ETL listing on a mop sink verifies structural integrity, manufacturing consistency batch-to-batch, and compliance with North American electrical and mechanical safety codes. It is the equivalent of UL listing for industrial equipment.

Both labels are stamped on the underside of the basin and on the spec sheet. Take a photo of both labels during install and keep it with your kitchen records - inspectors sometimes ask to see proof of certification on commissioning.

Installation Sequence (Atosa Spec)

1. Level the unit. Set the sink in position, place a 24-inch spirit level across the top of the bowl front-to-back AND side-to-side. Adjust each ABS bullet foot until both axes read perfectly level. Recheck after filling the basin with water once - the slab can settle slightly under load.
2. Plumb the drain. Connect the 3-inch drain tailpiece to a P-trap with cleanout. Use Teflon tape on all threaded joints and tighten until snug then a quarter turn. Test for leaks before closing the wall.
3. Wall-anchor the unit. Although the sink is floor-supported on its legs, anchor the back rim to the wall with two stainless lag bolts through the splash. This prevents the unit from shifting forward when an operator leans into the bowl to tilt a heavy bucket.
4. Install the faucet separately. The MRS-1-MOP ships without a faucet. Order a wall-mount commercial service-sink faucet with atmospheric vacuum breaker, 8-inch on-center supply, and pail hook. Verify spout height clears the flood rim by at least 1 inch.
5. Test under load. Fill the basin to the rim and verify no leaks at the bowl-to-tailpiece joint, the trap, or the wall connection. Drain and time it - a clean install empties a full basin in under 45 seconds.

Freight Minimum and Will-Call Pickup Locations

Atosa freight policy on the MRS-1-MOP requires a minimum of 6 units for standard LTL freight delivery. Single-unit buyers pick up at one of our regional Will-Call distribution centers:

• Los Angeles, CA
• San Francisco, CA
• Orlando, FL
• Chicago, IL
• Denver, CO
• Dallas, TX
• Boston, MA
• Newark, NJ
• Atlanta, GA
• Houston, TX
• Cleveland, OH

Call (206) 419-5801 before placing a single-unit order to confirm Will-Call availability and reserve your pickup window. Most warehouses release units within 48 hours of payment clearance.

Maintenance Schedule for the MRS-1-MOP

• Daily: Rinse the bowl with hot water after final shift to clear residual floor chemicals. Pull the strainer, rinse out mop strings and grit.
• Weekly: Spray a quat-based sanitizer on the bowl walls and creased drain board. Wipe down the galvanized legs and check for any moisture pooling at the foot. Pour 2-4 oz of ATDM Drain Maintainer down the drain after closing.
• Monthly: Inspect the galvanized legs for rust spots. Touch up any nicks with cold-galv compound. Verify the ABS feet are tight in the threaded sockets.
• Annually: Re-tighten the wall anchor bolts. Snake the drain line professionally. Replace the strainer basket if the welded mesh has corroded or distorted.
• Never: Use steel wool or wire brushes on the stainless bowl. The carbon steel particles embed in the surface and rust within weeks, leaving permanent orange stains.

What's Not Included

The MRS-1-MOP ships as a sink unit only. Plan for these additional purchases:

• Wall-mount service-sink faucet with vacuum breaker ($95-$260)
• P-trap and 3-inch drain tailpiece ($35-$60)
• Stainless lag bolts for wall anchor ($10)
• Floor drain in the janitor closet (separate fixture, $80-$200 part plus install)
• GFCI outlet on the wall above (if powering a wet-vac or scrubber charger)

Budget $250-$500 total for accessories plus labor on top of the $589 unit price for a complete code-compliant install.

Mop Sink Faucet Height: The Code Rule That Trips Up Every Buildout

The single biggest plumbing-code violation on mop sinks is faucet height and vacuum breaker placement. Get this wrong and you fail inspection no matter how nice the rest of the install looks.

The Rule

Per UPC §603.5.7 and IPC §608.13: the spout outlet of a mop sink faucet must terminate at least one inch above the flood-level rim of the receiving basin, AND a vacuum breaker (atmospheric or pressure type) must be installed on the supply line at least six inches above the highest possible water level in the basin.

In practice that means:

• Basin rim sits 10-12 inches above the floor (basin depth).
• Spout outlet must be at least 11-13 inches above the floor.
• Vacuum breaker must be 16-18 inches above the floor minimum.
• Real-world faucet body and spout sit 36-50 inches above the floor - much higher than a normal kitchen faucet.

What a Code-Compliant Mop Sink Faucet Looks Like

• Wall-mounted on 8-inch on-center supply lines
• Cast brass or chrome body with metal lever handles (no plastic on commercial)
• Atmospheric vacuum breaker (AVB) built into the body above the highest water level
• Integral wall brace or stop to prevent the spout from being yanked downward
• Pail hook on the spout for hanging a hose
• 3/4-inch garden-hose threads on the spout outlet for hose connection
• Optional bucket fill height adjustment

Common Faucet-Height Mistakes

1. Reusing a deck-mount kitchen faucet. Drops the spout below the flood rim - automatic violation. Always use a dedicated wall-mount service sink faucet.
2. Forgetting the vacuum breaker. The faucet body itself may have an integral AVB, or you may need to add a screw-on AVB to the spout - verify on the spec sheet.
3. Hose left attached to the spout submerged in the bucket. Even with a vacuum breaker, leaving a filled hose submerged below the flood rim creates a backsiphon hazard. Inspectors will write it up.
4. Mounting too low to clear a 35-quart bucket. Standard 35-quart bucket is 14 inches tall on casters. Spout needs to clear 16-18 inches above the floor minimum to fill without lifting.

Mop Sink Installation: Rough-In, Plumbing, and Permits

Rough-In Dimensions (Plumber's Spec Sheet)

Provide your plumber with these numbers before slab pour or wall framing:

• Hot and cold supply stub-outs: 28 inches above finished floor, 8 inches on-center, capped 1/2-inch copper or PEX
• Drain rough-in: 3-inch PVC or cast iron, P-trap stubbed up 2 inches above slab, centered to basin drain location
• Vent: 2-inch dry vent rising through the wall to roof or to a code-approved AAV
• Floor drain (separate fixture): 3-inch floor drain located within 6 feet of the mop sink, in the same closet, to capture overflow
• GFCI outlet: Optional but recommended on the wall above the sink for a wet-vac or auto-scrubber charger

Step-by-Step Installation

1. Set the basin on a clean, level slab. Shim any low corners with stainless or polymer shims - no wood.
2. Caulk the floor curb with NSF-listed mildew-resistant silicone where the basin meets the floor.
3. Thread the 3-inch drain tailpiece into the basin outlet with Teflon tape and a urethane gasket.
4. Connect the tailpiece to the P-trap below the slab using a 3-inch coupling. Hand-tighten then quarter-turn with channel locks.
5. Install the wall-mount faucet on the 8-inch on-center supply stubs. Use the rough-in plate that comes with the faucet to maintain spacing.
6. Verify the vacuum breaker is installed at the correct height (6+ inches above the flood rim).
7. Turn on hot and cold, check for leaks at every connection for 10 minutes under pressure.
8. Fill the basin to the rim and let it drain - watch for slow drainage or trap rumble that indicates a vent problem.

Permits and Inspections

Most jurisdictions require a plumbing permit for any new fixture installation including a mop sink. The inspector will check:

• P-trap presence and correct depth (2 to 4 inches of water seal)
• Vent rise within 6 feet of the trap (or AAV installed where allowed)
• Vacuum breaker height above flood rim
• Faucet spout 1 inch above flood rim minimum
• Floor drain in mop closet (if required locally)
• GFCI on any electrical outlets within 6 feet of the sink
• NSF label visible on the basin

Schedule the rough-in inspection BEFORE you close the wall. Schedule the final inspection AFTER the faucet is mounted and water is on.

Mop Sink Plumbing and Drainage

Drain Plumbing

The drain on a commercial mop sink works hard. Mop strings, grit, grease, food particles, and broken mop heads all try to make their way into the line. Design the drain right and you will not pay for a $400 emergency snake call every six weeks.

• 3-inch minimum drain pipe. Smaller pipe clogs within months.
• Removable stainless basket strainer at the basin outlet. Catches debris before it enters the line. Pull and rinse daily.
• P-trap below the basin with a cleanout plug on the back of the trap arm. Skipping the cleanout means cutting the wall open every time you have to snake the line.
• Branch to the building drain at 1/4 inch per foot slope. Too steep and water races past the solids; too shallow and the solids settle out.
• No connection to grease waste line. Mop sinks tie to the sanitary line, not the grease line. Grease interceptors are not designed for mop string and detergent foam.

Grease Trap Question - Can a Mop Sink Tie In?

No. Mop sink discharge bypasses the grease trap and goes directly to the sanitary sewer. Detergents and surfactants in mop water emulsify any grease in a trap, defeating its function and causing the trap to release oil into the public sewer. Most local plumbing codes prohibit the tie-in explicitly.

Supply Plumbing

• 1/2-inch copper, PEX, or CPVC hot and cold supply lines
• Stop valves on both lines accessible without removing finished material
• Hammer arrestors on both lines (mop sink faucets shut off fast and water-hammer commercial walls)
• Hot supply temperature limited to 140°F max at the fixture per most state codes
• Backflow protection at the fixture (vacuum breaker on the faucet) plus, in some jurisdictions, a reduced-pressure backflow preventer at the building main if the mop sink shares a chemical-injection system

Is a Mop Sink Required by Code? (Yes - Here's the Exact Language)

This is the most-searched mop-sink question on Google. The answer is yes, in virtually every food-service jurisdiction in the United States.

FDA Food Code §5-203.13

"At least one service sink or curbed cleaning facility with a floor drain shall be provided and conveniently located for the cleaning of mops or similar wet floor cleaning tools and for the disposal of mop water and similar liquid waste."

The FDA Food Code is adopted by 49 states (in various editions) and applies to every retail food establishment, restaurant, deli, food truck (when at a stationary commissary), grocery store, and institutional kitchen.

Uniform Plumbing Code §418.0 and IPC §418

"Each commercial kitchen, restaurant, hotel, bar, retail food, and similar occupancy shall be provided with not less than one service sink for the disposal of liquid waste from mop operations." Most western states adopt UPC; most eastern states adopt IPC. Both require it.

When the Code Says "or curbed cleaning facility"

A curbed cleaning facility is a tiled or stainless-lined floor receptor with a faucet above and a curb around it - basically a built-in shower stall for mop buckets. Acceptable substitute under FDA Food Code language. Some health departments accept it; some do not. Always confirm with your local health inspector before assuming a curbed facility passes.

When the Code Says a Mop Sink Is NOT Required

Limited exceptions exist:

• Mobile food units (food trucks) on the road - but the commissary they return to MUST have a service sink.
• Temporary food events under 14 days - disposable cleaning supplies may be permitted.
• Bed-and-breakfasts with fewer than 5 rooms in some states.

If your operation does not fit one of those tightly defined exceptions, plan on installing a service sink.

Restaurant Mop Sink: Best Practices for Daily Use

What Goes In a Mop Sink

• Dirty mop water and floor cleaning chemicals
• Mop heads (for rinsing after each shift)
• Floor squeegee, dustpan contents
• Auto-scrubber tank discharge
• Bucket-rinsing of food-truck or catering buckets

What Does NOT Go In a Mop Sink

• Food prep or dishes. Cross-contamination - never use a mop sink for any food contact.
• Handwashing. Even in an emergency, find a different sink. Inspectors will cite you on the spot.
• Fryer oil or solid waste. Send oil to a yellow grease bin. Mop sinks are not grease lines.
• Coffee grounds, vegetable scraps, ice. All clog the 3-inch drain over time.
• Bleach mixed with quat sanitizer or ammonia. Releases toxic chlorine gas in a confined closet.

Daily Cleaning Routine

1. End of shift: empty the bucket, rinse the basin with hot water
2. Spray a quat-based sanitizer on the basin walls and curb
3. Pull the strainer basket, rinse out mop strings and debris
4. Wipe down the faucet handles and vacuum breaker
5. Sweep the floor around the sink, mop the closet floor with fresh water
6. Hang mop heads bristles-up to dry - never leave them sitting in the basin

Weekly Drain Maintenance

Pour 2-4 ounces of Atosa ATDM Drain Maintainer down the drain after the last shift each week. The enzymatic formula digests grease and protein residue inside the trap and branch line, preventing the slow odors that develop in any mop sink line. Run the water for 30 seconds, then leave overnight without flushing.

Avoid pouring concentrated bleach or caustic drain cleaner into the drain - they kill the biological action of any enzyme product and corrode older cast-iron lines.

Where to Buy a Commercial Mop Sink (And What to Pay)

Price Ranges

Type	Typical Price	Notes
24x24 floor-mount stainless	$420 – $750	Most common in restaurants. Atosa MRS-1 sits at $589.
24x36 floor-mount stainless	$650 – $1,100	Larger bucket capacity, hotel use.
36x36 floor-mount stainless	$1,150 – $1,900	Production kitchens and institutional.
Corner mop sink	$580 – $950	Tight-space retrofits.
Mop sink faucet (wall-mount with vacuum breaker)	$95 – $260	Sold separately on almost every mop sink.
Molded stone mop receptor	$380 – $700	Heavier and harder to install; non-food use mostly.
Fiberglass utility tub	$180 – $340	Light commercial only, not recommended for kitchens.

Where The Restaurant Warehouse Fits

We carry the Atosa MRS-1 in stock at $589 with free freight shipping to commercial addresses in the lower 48. For larger 24x36 and 36x36 Atosa basins, contact us at (206) 419-5801 - we drop-ship from the manufacturer on a 7-10 business-day lead. We also stock ATDM Drain Maintainer for ongoing drain care.

Financing

If you are outfitting a new restaurant from scratch, the mop sink usually rolls into the full kitchen package. We offer 0%-down equipment financing on orders over $3,500 - most full kitchen buildouts qualify. Apply online or call us.

How to Make a Mop Sink Last 15+ Years

Stainless Steel Care

• Rinse the basin daily - standing chlorine bleach pits 304 stainless within months
• Never use steel wool, wire brushes, or scouring pads (they transfer carbon steel particles that rust)
• Use a nylon-bristle brush and a non-chloride degreaser for weekly deep cleans
• Wipe dry after cleaning to prevent water spots and mineral buildup from hard water
• Apply a stainless polish (food-grade mineral oil) monthly to maintain the passive layer

Faucet and Vacuum Breaker Maintenance

• Lever handles loosen every 6-12 months - tighten the set screws with an Allen key
• Vacuum breakers leak when the rubber check valve dries out; replace the cartridge every 3-5 years ($12-$20 part)
• Aerator screens (if present on the spout) clog with sediment; remove and rinse quarterly
• Drip from the spout means a worn ceramic disc cartridge - replace, do not just retighten

Drain Line Maintenance

• Pull the strainer and rinse daily
• Pour 2-4 oz ATDM Drain Maintainer weekly after final shift
• Snake the line professionally once per year - $150-$300 preventive cost beats a $600 emergency call
• Check the P-trap cleanout plug annually - replace the gasket if it shows wear
• Inspect the floor drain in the closet quarterly - clogs there cause floods, not just slow drainage

When to Replace

A 304 stainless mop sink lasts 15-20 years with normal maintenance. Replace when you see:

• Pinhole rust through the basin floor (usually starts under the strainer where standing water sits)
• Cracked welds at corner seams that leak even after re-caulking
• Basin pulling away from the floor curb (foundation issue, not the sink)
• Drain outlet threads stripped from repeated repairs

Top 10 Mop Sink Mistakes Restaurants Make

1. Specifying a deck-mount faucet. Almost always fails inspection because the spout sits below the flood rim. Use a wall-mount service-sink faucet only.
2. Forgetting the vacuum breaker. $42 part causes 70% of mop-sink inspection failures.
3. Routing the drain into the grease line. Defeats the grease trap and triggers a city violation.
4. Buying a fiberglass utility tub to save $200. Stains permanently, cracks under bucket impact, replace within 3 years.
5. No floor drain in the mop closet. First major overflow floods the kitchen.
6. Closet too small to operate. Need 24 inches of standing room in front of the basin plus 4 inches on each side.
7. Mixing chemicals in the basin. Bleach + ammonia = chloramine gas. Bleach + quat = also bad. Use one chemical at a time.
8. Using the mop sink for handwashing. Health code violation and a foodborne illness vector.
9. Skipping enzyme drain treatment. Mop strings build up inside the trap arm and cause periodic backups.
10. Not labeling chemical containers stored above the sink. OSHA HazCom citation - every container needs a GHS label even if it is just diluted bleach.

Related Sink Guides

A mop sink is one piece of a code-compliant restaurant plumbing layout. Pair it with these for a complete buildout:

• The Complete Three-Compartment Sink Guide - wash, rinse, sanitize for every dish your kitchen produces
• Best Commercial Hand Sinks Guide - every dedicated handwashing station required by code
• Shop All Commercial Sinks - full catalog with filters by compartment count and size
• 3-Compartment Sink Collection
• 2-Compartment Sink Collection
• 1-Compartment Sink Collection
• Hand Sink Collection

Frequently Asked Questions

What is a mop sink?

A mop sink is a low, deep stainless steel or molded basin built for filling mop buckets and dumping cleaning water in commercial kitchens. It is also called a service sink, mop basin, janitor sink, or janitorial sink. Federal Food Code and state plumbing codes require one in every restaurant and food establishment.

Is a mop sink required by code?

Yes. FDA Food Code §5-203.13 requires every food establishment to have at least one service sink or curbed cleaning facility for mop water disposal. UPC §418 and IPC §418 require the same. The few exceptions are mobile food units on the road (their commissary still needs one), short temporary events, and small B&Bs in some states.

What is the difference between a mop sink and a floor sink?

A mop sink has a basin with walls and a faucet for filling buckets. A floor sink is a flush-mounted indirect waste receptacle - it sits in the floor and receives drain lines from refrigeration and steam equipment via an air gap. You cannot fill a mop bucket from a floor sink because it has no faucet.

How tall should a mop sink faucet be?

The spout outlet must terminate at least 1 inch above the flood-level rim of the basin, with a vacuum breaker installed at least 6 inches above the highest possible water level. In practical terms the spout sits 36 to 50 inches above the floor. Always use a wall-mount service-sink faucet, never a deck-mount kitchen faucet.

What size mop sink do I need?

Most restaurants use a 24x24x10-inch floor-mount basin that fits a standard 26-quart mop bucket. Mid-size operations step up to 24x36. Hotels and production kitchens use 36x36. Whatever size you pick, leave 4 inches of clearance on each side and 24 inches of standing room in front.

Can a mop sink go in a bathroom?

Most health departments prohibit it. The mop sink must be in a separate janitor closet or service area, not inside a restroom used by staff or customers. Cross-contamination risk and OSHA chemical-storage rules drive the separation.

Can you dump mop water in a regular sink?

No. Dumping mop water in a hand sink, prep sink, or warewashing sink is a direct health-code violation in every state. Mop water carries food soils, bacteria, and chemicals that contaminate food-contact surfaces. The mop sink (service sink) is the only approved fixture.

What kind of faucet does a mop sink need?

A wall-mount commercial service-sink faucet with an integral atmospheric vacuum breaker, cast brass or chrome body, metal lever handles, 8-inch on-center supply connections, and a pail hook on the spout. Spout typically has 3/4-inch garden-hose threads for connecting a fill hose.

What size drain does a mop sink need?

3 inches. Anything smaller clogs with mop strings and debris within months. The P-trap should be 3 inches deep with 2-4 inches of water seal, and a 2-inch vent should rise within 6 feet of the trap.

Does a mop sink need a vent?

Yes. Every plumbing fixture connected to a sanitary drain needs a vent to prevent siphoning of the trap seal and to release sewer gas. Use a 2-inch dry vent rising through the wall to roof, or an air admittance valve (AAV) where allowed by local code.

Can a mop sink share a drain with a grease trap?

No. Mop sink discharge bypasses the grease trap and goes directly to the sanitary sewer. Mop water contains detergents that emulsify grease in the trap, defeating its function. Most local plumbing codes specifically prohibit this connection.

What is the rough-in for a mop sink?

Hot and cold supply lines 28 to 32 inches above finished floor, 8 inches on-center, stubbed out in 1/2-inch copper or PEX with stop valves. Drain rough-in is a 3-inch P-trap centered to the basin outlet, with a 2-inch vent rising to roof. A separate 3-inch floor drain in the closet handles overflow.

How much does a commercial mop sink cost?

A 24x24-inch 18-gauge stainless mop sink runs $420 to $750. The Atosa MRS-1 sits at $589 with free shipping. Step up to a 24x36 and budget $650 to $1,100. A 36x36 hotel-size basin is $1,150 to $1,900. Plan an additional $95 to $260 for the wall-mount faucet - they are almost never bundled.

How do I install a mop sink?

Set the basin on a level slab, caulk the curb with NSF silicone, thread the 3-inch drain into the basin outlet, connect to the P-trap, install the wall-mount faucet on 8-inch on-center supply stubs, verify the vacuum breaker is at correct height, pressure-test all connections, and fill-drain test the basin. Pull a plumbing permit and schedule rough-in and final inspections.

Can I install a mop sink myself?

Setting the basin is straightforward DIY. Connecting it to the building plumbing usually requires a licensed plumber and a city permit. Most jurisdictions require licensed work on any new fixture installation. The faucet alone needs vacuum-breaker placement that inspectors will check, so unless you are a journeyman plumber, budget $400-$800 for a pro install.

What is the difference between a mop sink and a utility sink?

A mop sink (service sink) has a low floor-mount basin with a wall-mount faucet 36+ inches above the floor and a vacuum breaker - built for filling mop buckets and code-compliant for restaurant use. A utility sink (laundry tub, slop sink) is a general-purpose deep sink on legs or a wall. Some jurisdictions allow utility sinks for janitorial duty if equipped with a vacuum breaker, but most new food-service construction requires a true mop sink.

Can a corner mop sink be installed in a small closet?

Yes. Triangular corner mop sinks save about 30 percent footprint compared to a square unit. They typically have a 24-inch leg on each wall, fitting closets as small as 30x30 inches with bucket clearance in front. Useful in converted historic buildings.

Where should mop water be disposed?

Down the mop sink (service sink) only. This is the explicit answer health inspectors want when they ask. Never the hand sink, prep sink, warewashing sink, or floor drain. The mop sink discharges through a sanitary sewer line designed for that load.

How often should a mop sink be cleaned?

At the end of every shift. Empty the bucket, rinse the basin with hot water, spray a quat-based sanitizer on the walls and curb, pull the strainer and rinse out debris, wipe down the faucet handles and vacuum breaker, and hang mop heads bristles-up to dry. Once a week pour 2-4 oz of enzyme drain maintainer into the drain after the last shift.

What is the best mop sink for a restaurant?

For restaurants under 3,000 sq. ft. the Atosa MRS-1 24x24 18-gauge stainless mop sink at $589 is the best value. It is NSF-listed, 304 stainless, welded one-piece construction, ships free, and fits a standard 30-inch janitor closet. Larger operations should size up to 24x36 or 36x36 in the same Atosa line.

Does a mop sink need GFCI protection?

The mop sink itself does not, but any electrical outlet within 6 feet of it must be GFCI per NEC §210.8. That includes the outlet for your wet-vac, auto-scrubber charger, or closet light fixture. Plan a GFCI duplex on the wall above the basin during rough-in.

Can a mop sink be outside?

In most jurisdictions, no. Mop sinks must be inside a conditioned space connected to building plumbing, with a backflow-protected supply and a vented sanitary drain. A few warm-climate states allow exterior installations under specific conditions (heated supply lines, freeze-resistant trap, locked enclosure). Always check your local code before assuming an outdoor install is legal.

What is the difference between 18-gauge and 16-gauge stainless steel?

In the stainless steel gauge system, 16-gauge is thicker than 18-gauge - lower number equals thicker steel. 16-gauge gets used on high-impact prep tables and three-compartment sinks where dropped pots are routine. 18-gauge is the industry standard for mop sinks like the Atosa MRS-1-MOP. It provides plenty of durability for utility tasks without the weight or cost premium of 16-gauge. For a janitor closet, 18-gauge is the right spec.

Can the ABS bullet feet on a mop sink be replaced?

Yes. The ABS bullet feet on the Atosa MRS-1-MOP and most commercial mop sinks are standard threaded inserts. If a foot cracks under load or strips out from over-tightening, unscrew it and thread in a replacement. The job takes 30 seconds with a 7/16-inch wrench. Order replacements through Atosa or any commercial restaurant parts supplier - the threads are usually 3/8-16 or 1/2-13.

Does the Atosa MRS-1-MOP come with a faucet?

No. The MRS-1-MOP ships as a sink unit only. You purchase the faucet separately based on your plumbing rough-in and code requirements. Plan for a wall-mount commercial service-sink faucet with atmospheric vacuum breaker, 8-inch on-center supply connections, metal lever handles, and a pail hook on the spout. Budget $95 to $260 depending on brand and feature set.

Why is one-sheet construction important on a mop sink?

One-sheet construction means the entire basin is formed from a single piece of stainless steel with no internal welds or seams inside the bowl. Welds are the first place a utility sink fails - they harbor bacteria, accumulate mineral deposits, and eventually corrode or leak under chemical exposure. By eliminating internal welds, one-sheet construction (as on the Atosa MRS-1-MOP) produces a more hygienic, longer-lasting product and meets NSF cleanability requirements more easily.

What cleaning agents are safe for an 18-gauge stainless mop sink?

Safe daily cleaners include mild detergents, quat-based sanitizers, neutral floor cleaners, specialized stainless steel polishes, and diluted chlorine bleach (rinse within 10 minutes of application). Never use hydrochloric acid (muriatic), nitric acid, abrasive scouring powders, or steel wool - all of these damage the passive chromium oxide layer that gives stainless its corrosion resistance. For drain care use enzyme-based maintainers rather than caustic drain openers.

About the Author

Sean Kearney is the founder of The Restaurant Warehouse and has spent 20+ years outfitting restaurants, breweries, ghost kitchens, and food trucks across the United States. He works directly with operators on equipment selection, plumbing layouts, and code-compliant kitchen design. Reach him at (206) 419-5801 or therestaurantwarehouse@gmail.com.