What Is a Grease Interceptor and When Is It Required?
A grease interceptor (grease trap) separates fats, oils, and grease from kitchen wastewater before it reaches the sewer — required by plumbing code and local sewer agencies for every commercial food-service establishment. Without one, grease solidifies in sewer lines, causing blockages the municipality fines you for. The plumbing engineer sizes it from the fixture count and menu type; the health department and sewer agency both review it.
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Sizing and types
Small under-sink traps serve single fixtures; hydromechanical interceptors handle small cafes; gravity interceptors (500-5,000+ gallon concrete or fiberglass tanks buried outside) serve full restaurants. Sizing follows the plumbing code's fixture-unit method or the sewer agency's formula — undersized interceptors pass grease and draw fines; oversized ones cost more to pump. The engineer coordinates the size with the kitchen equipment plan.
Location and installation
Gravity interceptors go outside, buried, with traffic-rated lids in drive areas and accessible for pump trucks — the civil engineer sites it clear of utilities, foundations, and easements. Indoor interceptors need ventilation and floor drainage for servicing. The plumbing drawings show the interceptor, all connected fixtures, and the sampling port many agencies require for compliance testing.
Maintenance and enforcement
Interceptors must be pumped when grease and solids reach 25% of capacity — typically every 1-3 months for busy restaurants, with manifests kept for the inspector. Sewer agencies conduct surprise inspections and sample effluent; violations bring fines and can trigger a requirement to upsize. Maintenance contracts with licensed haulers are standard; the cheapest interceptor is the one that gets pumped on schedule.
The bottom line
Every commercial kitchen needs a grease interceptor sized by the plumbing engineer and approved by the sewer agency. Size it right, site it for pump-truck access, and pump it on schedule — inspectors check.
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