Short definition
A laundry sink — also called a utility sink, slop sink, or laundry tub — is a deep free-standing basin used for hand-washing laundry, pre-soaking, mopping, and other messy work. The residential standard is a plastic or fiberglass tub on four adjustable legs, drained through a 1½-inch trap to the same waste system as a kitchen sink.
What it is
A typical laundry sink is a single-bowl plastic or fiberglass tub, about 22 inches across and 12 to 15 inches deep, sitting on four screw-down legs that adjust from roughly 28 to 34 inches in finished height. It has its own faucet — often a wall-mount swing-spout, sometimes a deck-mount kitchen-style faucet — and a basket-strainer drain that connects to a 1½-inch P-trap.
Drain rough-in is lower than a kitchen sink — typically about 13 inches above the floor, since the laundry-sink bowl is deeper and the drain enters the bottom. Trap size is 1½ inch, matching kitchen and tub. DFU load is 2 under the Uniform Plumbing Code that Washington adopts.
Laundry sinks often share a wall — and sometimes a trap — with the washing machine standpipe. In some configurations the washer drains over the rim of the sink instead of into a separate standpipe; whether that’s code-acceptable depends on the local jurisdiction’s UPC amendments and on the trap size handling the discharge volume.
The commercial cousin is a mop sink (floor-set, high curb) or a service sink (a deep-bowl floor-bolted basin with an integral stand trap). Those are mostly janitorial; in a residential garage or basement laundry, you have a free-standing utility sink on legs.
Why it matters to a homeowner
The laundry sink is the most abused fixture in the house. Cast-iron pots get scrubbed in it, paint rollers get rinsed in it, gardening tools soak in it. Two practical things to know:
It’s a freeze risk in WA. Most laundry sinks live in unheated or marginally-heated garages and basements, and the trap can freeze in a Puget Sound cold snap when nothing else in the house does. A heat-tape wrap on the exposed trap, or relocating the trap to a conditioned space, is a one-time fix for what otherwise becomes an annual February panic.
It has a unique clog profile. A plumber pulling a laundry-sink trap typically finds it ankle-deep in lint and detergent residue. If you have a washer draining into the sink (over the rim) rather than into a separate standpipe, that lint accumulates fast. Periodic trap-pull-and-rinse is reasonable preventive maintenance.
The other freeze-and-leak combination — a hairline crack in the bowl from a dropped cast-iron pot — is unfixable. Plastic and fiberglass laundry sinks are cheap; replace the whole sink rather than patching.
Common failure modes
- Cracked plastic bowl from impact. Replace the sink — patches don’t last.
- Frozen trap in unheated garages and basements during a Puget Sound cold snap. Insulate the trap or wrap with heat tape; long-term, move the trap inside the conditioned envelope.
- Drain clog from lint and detergent — pull and rinse the trap.
- Sink rocks on its legs — adjustable legs back off; level and snug periodically.
- Standpipe-discharge backflow into the sink — if the washer and sink share a downstream trap and a clog develops, soapy water can back up into the lower fixture. Indicator that the trap configuration is undersized or improperly vented.
Common variants and what a laundry sink is not
- Laundry sink vs. kitchen sink. Same 1½-inch trap, different rough-in height, different bowl depth. A laundry sink is deeper.
- Laundry sink vs. mop sink. Mop sinks sit at floor level with a high curb; commercial. Residential laundry sinks stand on legs.
- Laundry sink vs. cabinet-mounted utility sink. Modern remodels sometimes drop a deep stainless utility sink into a base cabinet — same plumbing as a kitchen sink with a deeper bowl.
- “Slop sink” terminology. Older usage; means the same as laundry or utility sink in residential context.