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Requirements for Your City

What Is a Grease Trap?

A grease trap is a plumbing device installed between a commercial kitchen and the municipal sewer. It uses gravity to separate fats, oils, and grease (FOG) from wastewater before they enter the sewer system. FOG floats to the top of the trap, solids settle at the bottom, and cleaner water exits through a middle outlet.

Every food service establishment in the United States that produces FOG is required by local plumbing code and municipal ordinance to install and maintain a grease trap. The U.S. Environmental Protection Agency identifies FOG as the leading cause of sanitary sewer overflows (SSOs) nationwide, which is why enforcement has tightened in most major US metros since 2024.

How Grease Traps Work

As warm kitchen wastewater enters the trap, it slows down enough for three things to happen. First, FOG cools and congeals, floating to the surface. Second, heavier solids sink to the bottom. Third, the middle layer — relatively clean water — exits through an outlet pipe to the municipal sewer. The trap must be pumped periodically before the combined FOG and solids reach 25 percent of its total capacity.

For a detailed explanation with diagrams, read our guide on how grease traps work.

The Rules That Actually Apply to Your Restaurant

FOG compliance has three regulatory layers. The US EPA sets pretreatment standards under 40 CFR Part 403. Each state adopts a plumbing code — either the International Plumbing Code (IPC) or the Uniform Plumbing Code (UPC) — that governs sizing and installation. Finally, cities and counties set the specific ordinances that dictate pumping frequency, permits, fines, and record-keeping.

In practice, local rules matter most. A Houston restaurant faces different pumping frequency and permit fees than a Los Angeles restaurant, even though both states use different plumbing codes. Our city requirements database tracks the exact rules for 246 US cities.

The 25 Percent Rule

The most commonly cited compliance threshold is the 25 percent rule: a grease trap must be pumped before the combined FOG and settled solids reach 25 percent of the total liquid depth. Some cities add a 50 percent rule on the settled sludge layer alone. Exceeding either threshold at inspection triggers a Notice of Violation and typically a fine. See our guide to the 25/50 rule for how inspectors measure it and what happens when you fail.

Consequences of Non-Compliance

Typical first-offense fines range from $500 to $2,500. Repeat violations can escalate to $10,000+ per day. Severe discharges that cause sanitary sewer overflows into waterways can trigger federal Clean Water Act penalties up to $25,000+ per day. Non-compliance can also result in permit revocation, which effectively closes your kitchen until the issue is resolved.