What is actually happening
A grease trap works by slowing water down so grease can float and solids can sink. When the grease cap thickens past the working volume, the inlet baffle starts pushing new water into a layer of fat instead of a layer of water. Flow drops, the sink drains slowly, then the sink does not drain at all. The timing feels malicious — Friday, 7:40 pm — because that is when the most hot, greasy water hits a trap that was already full on Thursday.
What to do in the next hour
- Stop sending water down. Pull the drain plugs, move dish to the hand sink if you have one, and do not run the dishwasher. More water on a blocked trap ends up on the floor.
- Do not pour anything in. Boiling water re-melts the cap and sends liquid grease downstream — straight into the discharge Richmond caps at 100 ppm. Degreasers and enzymes do the same thing more slowly.
- Lift the lid and look. If the grease layer reaches the outlet baffle, the trap is full. If the layer is thin and the sink still will not drain, the blockage is in the line past the trap — a different truck.
- Call. Say what you saw under the lid. That one detail decides whether you need a pump-out or a jetter.
Why this is a compliance event, not just a plumbing one
Richmond does not regulate grease by calendar; it regulates by what leaves your pipe. A trap that is full enough to back up a sink has been discharging over the standard for a while. City code lets the Department of Public Utilities inspect at any time and bill you for treating what you send them. The backup is the visible symptom; the discharge is the regulated one.
Keeping it from happening again
Run the frequency calculator with your real trap size and covers. If the interval it suggests is shorter than the one you have been keeping, that gap is the whole story. The fix is a schedule, a full three-layer evacuation each time, and a receipt in the folder.