Grease traps are designed to allow the separation of grease and solids from wastewater. As water and grease from a sink or dishwasher enter a grease trap, the turbidity of the mixture eventually subsides to a point where the grease, which is lighter than water, will accumulate and float on the water's surface.

A special piping configuration in the grease trap allows the water to enter and exit below the level of the floating grease, thus providing a space for the grease to collect. Grease traps provide an effective means of grease removal if they are pumped out regularly.