Wastewater is taking the easiest way out. The usual causes are a trap or interceptor past its cleaning date, grease coating the line downstream, or a blockage in the sewer line. Stop water use, get the device pumped, then have the line jetted and camera-checked before the next dinner rush.
Do this first
- 1Stop sending water down the grease line: pause the dish machine, sinks and mop water.
- 2Keep food out of the affected area and shut off equipment that drains to it, if the water is spreading.
- 3Call your pumper and a plumber. Do not pour enzymes, solvents or emulsifiers in. Phoenix prohibits them, and Chandler says these products only emulsify grease temporarily, until it re-congeals farther down the pipe.
Why it happens
Phoenix's FOG manual explains the mechanism. FOG hardens and builds up until it blocks the city sewer or your own line. When that happens, sewage coming from upstream backs up and finds another way out, through a manhole, or through a drain or clean out on the property.
That points to three usual causes:
- The device is full. Phoenix says most interceptors stop working well when fats, oils and solids reach 25 percent of capacity. Chandler says that if grease is seen leaving the device, the cleaning frequency must increase. See the 25 percent rule.
- The pipe after the device is coated. Grease that passes the device sets up on the pipe wall until the line narrows. Tempe calls the extreme version a fatberg.
- A blockage further down the sewer. If so, even a freshly pumped device has nowhere to send its water.
How to tell which one
A pumper who empties the device first tells you a lot. If the floor sinks drain once it is empty, the device was the problem. If they still back up, the blockage is in the pipe. A camera run shows what is coating or blocking it, and jetting clears it. Our page on pumping vs cleaning vs jetting explains which service fixes which.
Keep it from coming back
Follow the city's pump schedule and keep the invoices. Scrape plates and pans dry, keep screens in the drains, and watch what goes into the trap. For the wider picture on repeat overflows, read why a commercial kitchen drain keeps overflowing and why a floor drain backs up. For a backed-up drain or sewer line, HQ offers 24/7 emergency service and gives the price before work starts.
For the smell that often comes with a backup, see how to control odor from a grease trap or interceptor.