A slow hand sink usually has a local blockage in its trap or short branch, because it carries soap and light solids. A slow mop sink is more often packed with mop debris, grit and grease. If a clean trap does not help, or other fixtures slow too, the restriction is farther down the line.
The hand sink
A hand sink carries soap, water and the odd bit of paper towel or glove. A slow one is almost always a partial blockage in its own trap or the short branch behind it. Phoenix's FOG manual lists the fixtures that count as grease-bearing in a kitchen and then adds "Hand wash sinks do not apply," which fits what you see in practice: the clog is rarely grease.
It still cannot wait. Maricopa's construction guide says hand sinks "must be easily accessible with no barriers or obstructions that restrict accessibility," and a sink that will not drain can end up out of service. What a restaurant does when a required handwashing sink stops working covers that side.
The mop sink
Mop water is a different load. The guide says "Mop water and similar liquid wastes are contaminated with microorganisms and other filth," and a mop basin collects string, grit, food scraps and floor-cleaning residue. Phoenix's manual lists mop sinks among the grease-bearing fixtures in the kitchen prep or wash area, so mop water that carries kitchen grease adds to the load. The same guide says food service equipment sinks and service (mop) sinks cannot receive the discharge of another sink's indirect waste pipe, so a mop sink should never be the workaround for a slow prep sink.
Sorting a local clog from a line problem
- Only that sink is slow. Clean the strainer and trap. If it clears and stays clear, you are done.
- It returns within days. The branch line behind the trap is narrowing. A cable or jet clears it, and a camera shows why.
- Floor sinks or other fixtures slow at the same time. Treat it as a line or interceptor issue, not a sink issue. Floor sinks, floor drains and mop sinks explains how they share lines, and what a commercial drain cleaning visit involves shows what to expect.
What helps
Put a strainer in the mop basin, dump solids in the trash first and keep fryer oil out of both sinks. Phoenix's manual says to "Install screens on all kitchen drains to keep food scraps from going down the drain." If a mop sink or hand sink keeps slowing after cleaning, we jet the line before open or after close and run a camera to see what is left. Estimates are free.