A standard grease interceptor is a large capacity underground vault with at least two chambers installed on the gray water discharge from a kitchen facility. The large capacity of the vault slows down the wastewater, allowing oil and grease to float to the surface and solid material to settle out. These vaults are installed outside the building as near as possible to the source of oil/grease.
The vault has a concrete lid with manhole openings in the top. These allow access into the vault for cleaning and for inspection of vault components, and they allow for visual inspection of all interior baffle tees. These baffle tees are usually made of 6” PVC. Vault capacity is determined using a calculation provided in the Uniform Plumbing Code (see the most current version of UPC for calculation).
Grease traps are made of rust resistant metal and can be installed above or below the floor level, usually in the kitchen near the fixtures that discharge to them. A grease trap has a much smaller capacity than a grease interceptor vault.
A solid metal lid is usually affixed to the grease trap body with a screw on each corner, although some lids have one large screw or bolt in the middle of the lid. Some grease traps have a separate discharge section with a cleanout plug at the top of the section. Up to four fixtures can be connected to a grease trap, and the trap is sized according to the number of fixtures that can connect to it. Sizing criteria can be found in the Uniform Plumbing Code.