How Is a Commercial Grease Interceptor Sized Correctly?

Commercial grease interceptor sizing is the engineering of selecting interceptor capacity from the kitchen's grease-producing fixture flow rates using the code-required sizing method. It covers gravity versus hydromechanical interceptor types, retention time for grease separation, location and venting, local pretreatment and health department requirements, and pump-truck access for cleaning. The principle is separation time: grease floats, solids sink, and the water in the middle flows on to the sewer. Everything about the sizing — volume, flow rate limits, baffle arrangement — serves giving the wastewater enough quiet time in the tank for that separation to happen. Rush the water through and grease goes straight to the sewer.

Location is the first practical decision: close enough to the kitchen that the waste piping runs short and steep (grease congeals in long, flat runs), but positioned where a pump truck can reach the lids and where the lids don't sit in traffic. Venting follows code — interceptors need venting to prevent siphonage and pressure buildup, coordinated with the building's vent system. Piping details decide whether the interceptor works: the inlet and outlet piping, flow control fittings on hydromechanical units, and cleanouts that let the line be maintained. I also coordinate with the civil engineer on the underground installation — bedding, traffic loading on the tank and lids, and groundwater. A structurally failed interceptor is an environmental problem, not just a plumbing problem.

A complete grease interceptor design satisfies the sizing math, the local authority, and the pump truck driver. Here's what I verify. Size it right, vent it right, and make sure it can be cleaned.

• Sizing by the book: fixture flow rates totaled per the local code's required method, with the right interceptor type
• Fixture mapping: every grease-producing fixture connected, clean-water fixtures kept out
• Location and access: short steep waste runs from the kitchen, lids reachable by pump truck, traffic loading handled
• Venting and piping: code-compliant venting, flow controls where required, cleanouts for maintenance
• Local approval: pretreatment program rules, sizing minimums, and submittal requirements confirmed upfront