Grease Trap /Smaller interceptors are meant for indoor connection to individual sinks and other fixtures (with a total flow of less than 50-100 gpm), whereas bigger interceptors are installed outside and underground to serve entire facilities. These distinct varieties are referred to as "trap" and "interceptor" interchangeably, however the smaller is sometimes referred to as a trap while the larger is referred to as an interceptor. In its most basic form, a grease trap slows the flow of warm or hot greasy water and allows it to cool. The grease and oil in the water split out as the water cools and floats to the top of the trap. The grease-free colder water continues to travel down the pipe to the sewage. Grease traps/interceptors separate FOG using one of two ways, each of which is best suited to certain uses. To separate FOG, which is about 80% lighter than water, the larger "passive" or "gravity" interceptors rely more on time and gravity. The "retention period" of these passive units is increased by larger tank sizes, internal baffling, and standpipes, enabling gravity to work its magic. Professionals normally clear out these interceptors on a regular basis.