Floor drains and floor sinks keep commercial kitchen floors dry and let equipment drain safely through an air gap. These answers explain the difference between them, indirect waste, venting and trap primers, sizing, installation, cleaning, and cost. Plumbing codes vary, so verify the details with your local authority.
A floor drain is a drain set into the kitchen floor at a low point, with a strainer grate on top and a trap below. Wash-down water, spills, and equipment overflow run across the sloped floor into it and out to the sanitary sewer. The trap holds water to block sewer gas. In commercial kitchens they keep floors dry, sanitary, and slip-resistant. Rules on quantity and placement vary, so verify local code/AHJ.
Floor drains move water off the kitchen floor quickly (from mopping, wash-downs, equipment condensate, and spills) so surfaces stay dry, sanitary, and slip-resistant. They also give a place for indirect waste from sinks and equipment to discharge through an air gap. Proper drainage is a health-code expectation, but the exact number and location of drains varies by jurisdiction, so confirm requirements with your plumber and AHJ during design.
The trap is the U-shaped section of pipe just below a floor drain that stays filled with water. That water seal blocks sewer gases and odors from rising into the kitchen. If a drain is used rarely, the trap can dry out and smell, which is why many codes require a trap primer to keep it topped off. A dry or missing trap is a common inspection finding and an easy fix.
The grate (or strainer) is the removable metal top of a floor drain. It supports foot and cart traffic while catching food scraps, debris, and packaging so they do not clog the line. Grates come in various sizes and load ratings, and heavy-duty versions handle rolling equipment. Clean grates regularly and keep them in place, because a missing grate is both a trip hazard and a fast route to a clogged drain.
A floor sink is a small, shallow basin recessed into the floor with its rim near floor level, used mainly as an indirect-waste receptor. Drain lines from sinks, dish machines, steam tables, and refrigeration terminate above it with an air gap, so wastewater falls into the floor sink and drains to the sewer. Its smooth, often porcelain-coated interior is easy to clean and resists the buildup that plain floor drains tend to collect.
Equipment that must drain indirectly discharges into a floor sink: typically prep sinks, the indirect leg of a three-compartment sink, dish machines, ice machines and bins, walk-in and reach-in condensate lines, steam tables, dipper wells, and combi ovens. Each line ends above the floor sink with an air gap so no contaminated water can siphon back into the equipment. Grouping this equipment near floor sinks keeps drain runs short and code-compliant.
An indirect waste connection means a drain line empties into a floor sink or funnel through an open air gap instead of being hard-piped to the sewer. The gap physically separates the equipment from the drainage system, so a sewer backup can never siphon dirty water into food equipment. The FDA Food Code requires indirect drainage for food, utensil, and ice-related equipment. Air-gap size rules vary, so confirm the minimum with local code/AHJ.
Refrigeration condensate and ice-machine or bin drains must discharge indirectly, usually into a nearby floor sink or funnel drain through an air gap, never hard-piped to the sewer and never onto the floor. Long horizontal runs should slope to drain and be insulated to prevent sweating. Locating a floor sink close to the walk-in and ice machine keeps these lines short. Requirements vary, so check your local plumbing code.
Yes. Like other drains, floor drains and their traps generally must be vented so water flows freely and the trap seal is not siphoned away. Venting can be an individual vent or, where allowed, a wet vent. Without proper venting, traps gurgle, drain slowly, and lose their seal, letting sewer gas in. Venting methods and sizing are code-specific, so have a plumber design them to your local code.
If a floor sink trap can dry out (for example one that only receives occasional condensate), a trap primer helps keep the seal full to block odors. A primer feeds a small amount of water to the trap automatically. Floor sinks receiving frequent flow may not need one. Whether a primer is required depends on use and local code, so confirm with your plumber and inspector during design.
In some jurisdictions a floor sink can be wet-vented (vented through the drain line of another fixture), but the rules are strict about arrangement and pipe sizing. Others require an individual vent. Wet-venting done wrong causes trap siphoning and odors. Because acceptance and configuration vary widely by plumbing code, do not assume it is allowed. Have a licensed plumber confirm the design with your AHJ before you build.
Drainage fixture units (DFU) are how plumbing codes rate the flow a fixture adds to the drain system, which then sizes the pipes. A floor sink or floor drain is assigned a value based on its outlet size, often around 2-3 DFU for a typical 2-inch or 3-inch floor sink, but the exact figure comes from the code table in force. Use your local code's values when sizing drainage.
Floor sinks come in standard footprints (often around 12 by 12 inches) with 2-, 3-, or 4-inch outlets. Pick a size and outlet that handle the combined flow of the equipment draining into it without overflowing, and leave room for multiple drain lines to reach it with air gaps. Half-grate versions let a pipe enter while keeping part of the basin open. Confirm outlet sizing against your local code and the equipment spec sheets.
Commercial floor drains commonly use 2-, 3-, or 4-inch outlets, with 3-inch a frequent choice for kitchens and larger pipe for heavy wash-down areas. The grate itself may be several inches to about a foot across. Pipe size is driven by the drainage fixture units it carries and the code table, not guesswork. Undersized lines clog and back up, so have your plumber size the waste pipe to local code.
A floor sink is set during slab work: the basin is positioned so its rim finishes flush with (or slightly below) the finished floor, the outlet ties into the building drain with a trap and vent, and the surrounding floor is sloped toward it. Tile or epoxy flooring is finished tight to the rim to prevent water intrusion. It is plumbing plus concrete and flooring work, so use a licensed plumber and expect a rough-in inspection.
Installing a floor drain in a slab means locating it at the floor low point, running and trapping the outlet pipe, adding a vent, setting the drain body at finished-floor height, and sloping the surrounding concrete toward the grate. In new construction it is placed before the pour; in a retrofit the slab is saw-cut and patched. Get the rough-in inspected before closing the floor, and follow local plumbing code throughout.
Yes. Many floor drains and floor sinks have adjustable or extendable tops that let the grate be raised or lowered to meet a new floor thickness during a remodel. If the range is not enough, the drain body may need to be reset, which means opening the slab. Getting the grate flush with the finished floor matters for drainage and to avoid trip hazards, so plan drain heights with your flooring installer.
To replace a grate, measure its outside dimensions (diameter, or length by width), the opening it drops into, and note whether it is square or round and how it fastens. Also check the drain brand and model if visible, since covers are often proprietary. Bring the old grate or a photo plus measurements when ordering, and choose a load rating that matches your traffic, because light-duty grates crack under carts.
Remove the grate and scrub the basin with a brush and detergent, clearing any food debris, then flush with hot water and sanitize; the smooth porcelain interior makes this easy. Do it daily or as needed, because floor sinks that collect food waste breed odors, flies, and slime fast. Keep the strainer in place and make sure the air-gapped lines above still discharge cleanly. Regular cleaning is a common inspection point.
Lift the grate, remove the strainer basket if present, and pull out debris. Many kitchen floor drains have a removable trap or bucket you can take out, empty, and scrub; otherwise flush with hot water and a drain brush. Enzyme or bio drain treatments help control grease and organics between deep cleans. Avoid harsh caustics that damage pipes. Cleaning traps regularly prevents the slow drains and odors inspectors notice.
You generally should not simply seal a floor drain solid, because codes often require a legal cap or removal by a plumber. An abandoned drain with a dry trap becomes an odor and pest pathway. If a drain is unused but kept, prime the trap periodically to hold the water seal. Permanently abandoning a drain usually means capping it below the floor per code, so check with your plumber and AHJ before covering one.
Many codes require either a drain pan piped to a drain or a floor drain beneath a tank water heater so a leak or tank failure does not flood the space. Commercial water heaters also need a safe route for temperature-and-pressure relief-valve discharge. Whether a floor drain, pan, or both is required depends on location and local code, so confirm with your plumber. See commercial kitchen hot water requirements.
Commercial dish machines discharge a lot of hot water, so they typically drain indirectly into a nearby floor sink or floor drain through an air gap rather than a hard connection. That prevents any backup from siphoning into the machine. The receptor must handle the flow without overflowing during the drain cycle. Placement and drain type follow the machine spec sheet and local code, so coordinate the floor sink location with the installer.
A smelly floor drain almost always means a dry trap: the water seal evaporated and sewer gas is coming up. Pour water down to refill the trap, and if it dries again, add a trap primer. Odors can also come from grease and food slime built up in the drain, which needs scrubbing and enzyme treatment. Persistent smells despite a full trap may signal a venting problem worth a plumber's look.
Clean floor drain grates and strainers daily, and give the drain body and trap a thorough scrub weekly or more often in heavy-use areas. Floor sinks that catch food or condensate may need daily attention. Regular cleaning prevents grease buildup, fruit flies, slime, and the odors and clogs that draw inspection deductions. Build it into your closing checklist so it does not get skipped during busy shifts.
Mop water can go down a mop sink or floor drain, but grease should not: fats poured down any drain congeal, clog lines, and violate FOG rules; cooled grease and fryer oil belong in a grease-recycling container. Even greasy mop water is better emptied into a mop sink connected through your grease system where required. Dumping grease down floor drains is a common cause of backups and citations.
Start by removing the grate and clearing debris and grease by hand, then plunge or use a hand auger (snake) to break up the clog downstream. Hot water and an enzyme treatment help dissolve grease. Avoid harsh chemical openers that damage pipes and endanger staff. If it keeps clogging or backs up at multiple fixtures, the main line or grease interceptor may be the problem, so call a drain professional.
The fixture itself is inexpensive, often $50-$300 for a floor drain or floor sink, but installation is where cost lands. In new construction, adding one during the pour is modest; retrofitting into an existing slab means saw-cutting, plumbing, patching, and inspection, commonly running several hundred to a couple thousand dollars each. Multiple drains and long pipe runs add up. Get local plumbing bids based on your layout.
No. A floor sink is a small, shallow floor-level receptor for indirect drainage from equipment. A mop sink (service sink) is a larger basin, floor-mounted or raised, with a faucet, used to fill buckets and dump mop water. They serve different purposes, though both connect to drainage. Most commercial kitchens need a mop sink for cleaning water plus floor sinks for equipment drainage, so check which your code requires.
Yes. A hand or drum auger (snake) is the standard tool for clearing a floor-drain clog beyond what removing debris fixes. Remove the grate and any trap bucket, feed the snake into the line, and work through the blockage, then flush with hot water. For recurring or main-line clogs, a professional with a powered auger or jetter is more effective. Skip caustic chemical openers, which harm pipes and staff.