Grease Traps 101

The City of Abilene has experienced a large number of sanitary sewer overflows (SSOs) for the past few years. An SSO results from a clog or blockage in the sewer line. When the line is clogged, the sewage must go somewhere and so it overflows to the next available outlet-a sink, manhole, dishwasher, etc. Most of the SSOs have been due to Fats, Oils, and Grease (FOG) in the sewer. In the photo at right, grease from a restaurant has overflowed outside. It can not only kill the grass and harm the environment, but kill a restaurant's budget.

  1. What Is a Grease Trap
  2. Why They Are Necessary
  3. Maintenance
  4. Good Kitchen Practices
  5. Pros & Cons of Small Grease Traps

A grease trap is a device that separates grease and solids from wastewater before it enters the sanitary sewer. Grease traps are installed as part of the plumbing at food service facilities such as restaurants and cafeterias.


There are two types of grease traps:

  • Small grease traps (50 gallons or less) are much smaller and are often located indoors under the three-compartment sink.
  • Large grease traps (more than 50 gallons) are usually located outside and typically have manhole type lids.

They both operate essentially the same way. Dirty, greasy water from kitchen sinks, dishwashers, etc. goes into the grease trap along with any food scraps that get washed down the drain. The mixture separates into three layers as it cools. Food scraps and solids sink to the bottom, grease floats to the top, and water ends up in the middle. As the grease layer and solids layer build-up, the water goes through a series of baffles and eventually to the outlet of the trap.


Workings of a Grease Trap

Some facilities also have a holding tank to recycle used frying oil, but this is not a grease trap since it’s not connected to the sewer system.