Grease interceptors are similar devices like a grease trap, but with a larger holding capacity, the capability of dealing with a larger amount of water flow. The device has two main components – the baffled structured trap with two compartments – primary & secondary, and a sludge tank. They follow the same principle of density and weight. Grease is less dense than water, and solids are heavier than the other two elements in the interceptor. So when wastewater gets slowed down by the baffling structure of the trap, and grease gets harder; they separate themselves into three layers. Less dense grease floats on top of the water in the top layer, heavier solids remain in the bottom and get stored in the sludge tank. Water stays in the middle layer, and after a particular time, gets allowed to leave the trap through a pipe to the drainage system.

There is no difference between a grease interceptor and a grease trap in the way they operate themselves. But there are few differences in their appearance, and capability to work (as mentioned earlier). Grease traps work well in smaller establishments that flush down less wastewater every minute and fit easily under any sink. But a grease interceptor was designed for larger businesses and has to be placed outside the building, usually in the parking lot or underground. Grease interceptors can handle more water flow (more than 50 gallons per minute). They have a larger holding capacity as well and can hold up to 2,000 to over 10,000 gallons of sludge in their tank which is way more than any grease trap. For their large holding capacity, grease interceptors require less cleaning operation than a grease trap. Cleaning a grease interceptor once every three months is fine, while a grease trap has to be cleaned every month or two.