A grease trap, sometimes called a grease interceptor, is a piece of restaurant equipment which is required in many regions to keep the sewers functional. The grease trap acts as a filter to remove fats and oils from water before it enters the municipal waste system. Since fats and oils can clog a sewer system, the use of a grease trap ensures that the sewer system runs smoothly. In a commercial kitchen, a grease trap treats all of the water coming out of the kitchen.

A properly equipped commercial kitchen usually has multiple sinks at prep stations, an industrial dishwasher, and large sinks for pre-treatment of dishes and other cooking tasks. The floors typically are sloped with central drains, allowing workers to clean the whole kitchen, and the kitchen may also have an in-house laundry facility. The combined drainage from all of these sources can be formidable, requiring a very large grease trap to ensure that water will drain smoothly.

A grease trap looks like a large box or barrel spliced into the water drainage line. When the water enters the grease trap, it cools down, allowing the lighter oil to precipitate out to the top. A series of baffles in the grease trap collect oil and chunks of material while the water sinks to the bottom. An exit pipe at the base of the grease trap allows the treated water to flow out, while the grease remains enclosed on top.

In order to function properly, a grease trap and its lines must be regularly cleaned and maintained. Staff can empty the grease trap by hand, or a company may be hired to pump out the grease trap. Some grease traps use automatic systems to skim out the grease and dump it into a container, but these grease traps still need to be periodically broken down and cleaned. All of the baffles of a grease trap should be scrubbed, and the drainage lines should be scoured to remove accumulated grease.

Efficiency will be lost if a grease trap is not cleaned regularly. Ultimately, the grease trap can clog, leading to backups of water into the kitchen. A cleaning rotation and log for the grease trap is usually kept, to ensure that it is kept operating in peak condition. Health inspectors may periodically check the grease trap as well, to assure themselves that it is working properly, and that all of the water in the establishment is being treated before draining into the sewer.