Under the Sink Grease Trap Installation

Understand the workings of a grease trap. FOG is lighter than water and so rises to the water's surface, where it's collected through a series of baffles. Any solid waste will fall to the bottom, allowing filtered water to flow cleanly from the sink to the drain. Study your specific trap to understand its operation. Schedule regular cleanouts to remove collected grease and get rid of any solids.

Install a grease trap, also called an interceptor, as close as possible to the source of the grease, typically a sink where pots and pans are emptied and cleaned. Use a strainer in or just under the sink drain to eliminate solids, such as food particles.

Position the input into the grease trap on the end of a P-trap, the U-shaped pipe directly under the drain. Fasten the grease trap input pipe to the P-trap output pipe; this connection may vary with the type of grease trap, but typically is a compression connector secured by tightening a screw collar. Tighten the collar by hand or with slip-joint pliers. Use teflon tape to secure the connection if the trap manufacturer recommends it.

Connect an air relief or vent opening on the grease trap to the vent pipe serving the sink's plumbing. Vent locations and connection will vary with the type and size of the trap, but all must be tied into a vent leading to the outside. Add PVC or similar pipe if necessary to reach from the trap vent to the plumbing vent pipe. Use compression connectors or whatever style of connection the trap maker recommends.

Hook up the grease trap outlet pipe to the pipe leading to the main drain and eventually to the sewer line. Make this connection at approximately the same level as the input; it typically will be behind a baffle blocking grease from the outlet, but allowing water to come up and drain out. Adjust the unit's flow control so water will run through the trap to eliminate waste but not flush out grease; most traps will have some control to regulate the volume of water entering the trap.