How Often Should a Grease Trap Be Cleaned? The 25 Percent Rule by City

Search this question and you get hauler blogs. Most say the 25 percent rule is an "internationally recognized standard" or an EPA requirement, then recommend cleaning "every one to three months." Neither claim is quite right. The rule has a specific origin, cities adopted it unevenly, and the calendar cap is a separate local decision. This page lays out what each city actually requires. Every figure here comes from a utility program page, an ordinance fact sheet, or a public bid tabulation, and the full 53-statistic dataset is on our restaurant grease trap and FOG statistics page.

Where the 25 percent rule comes from

Three layers govern a grease trap, and only the bottom one can enforce a number.

The federal layer is thin on purpose. According to the EPA's National Pretreatment Program fact sheet on food service grease (2012) (epa.gov), the regulation at 40 CFR 403.5(b)(3) prohibits "solid or viscous pollutants in amounts which will cause obstruction" in the treatment plant and its collection system. That is the whole federal position. It does not say 25 percent, and it does not say 90 days. The same fact sheet reports that a single restaurant produces 800 to 17,000 pounds of grease per year, counting trap waste and grease that escapes to the plant. That volume is why local utilities write their own rules.

The 25 percent number has a traceable origin. According to interceptor manufacturer Schier's explainer on the rule (schierproducts.com), the grease storage capacity of small hydromechanical interceptors at their minimum rating works out to 25 to 35 percent of depth. The industry adopted 25 percent as the conservative estimate. Schier attributes the first published statement to a 1998 Plumbing and Drainage Institute guide, which noted that interceptors certified to PDI-G101 may need maintenance when as little as 25 percent of rated capacity has been reached. Utilities then borrowed that threshold and wrote it into ordinances, sometimes by name. Louisville MSD's FOG guidelines (2015) (louisvillemsd.org) literally call it "the 25 Percent Rule."

So the honest answer to "is the 25 percent rule a law" is: it is a law where a city made it one. Elsewhere it is a rule of thumb. And several large utilities chose a different number entirely.

What 14 cities actually require

The table below pulls every jurisdiction our research team verified against the utility's own program page or ordinance fact sheet. "Not stated" means the source we checked does not give a figure, not that the city has no rule. The gauge shows the fill trigger; a hatched gauge means the city does not state one.

Each row is cited to the named utility's own page or PDF, fetched and read. The full row-by-row citations, with the quoted wording for every cell, live on the FOG statistics page.

A few rows deserve a closer look. Dallas is the cleanest example of the rule as law. According to Dallas Water Utilities' pretreatment program FAQ (2026) (dallascityhall.com), City Code Sec. 19-126.2(c) requires interceptors to be cleaned "as often as necessary but not less than every 90 days, or whenever 25% or more of the interceptor contains floating materials, sediment, oils, or grease." Two triggers, and whichever comes first wins.

Austin shows the rule is not universal even inside Texas. According to Austin Water's grease trap maintenance page (2026) (austintexas.gov), traps must be pumped at least every 90 days "or sooner if grease and solids make up 50% or more of the wetted height of the trap." A Texas charter school network's 2022-23 grease trap contract, tabulated by IDEA Public Schools (ideapublicschools.org), copied that 50 percent wording into its vendor scope rather than the 25 percent rule. St. Louis goes looser still. According to the Metropolitan St. Louis Sewer District's grease interceptor guidance (msdprojectclear.org), the district recommends cleaning "when 60 percent capacity is reached."

Houston skips the fill trigger on its public pages and enforces the calendar instead. According to the Houston Permitting Center's special waste generator page (2026) (houstonpermittingcenter.org), Code Sec. 47-512(b) requires every interceptor inside city limits to be fully evacuated at least quarterly unless a Notice of Waiver is approved. Seattle takes the opposite approach and defers to the equipment. According to Seattle Public Utilities' FOG guidance for commercial kitchens (seattle.gov), businesses clean per the manufacturer's specifications, and the 25 percent threshold applies only when no specification is available.

How fast a trap fills

The 25 percent rule is measured, not scheduled. The trigger is the depth of floating grease plus the depth of settled solids, divided by the total depth of the trap's contents. Dallas publishes a worked example in its interceptor brochure, and it is the clearest illustration of why a 90-day schedule can still fail an inspection.

How quickly a trap reaches that line depends on the trap and the kitchen, and no city we reviewed publishes a fill-rate formula. What the sources do give is sizing, which sets the denominator. According to Dallas Water Utilities' pretreatment FAQ (dallascityhall.com), a grease trap is the small indoor device, usually under 100 gallons, and a grease interceptor is the precast concrete tank of 250 to 5,000 gallons. According to Louisville MSD's FOG guidelines (2015) (louisvillemsd.org), minimum interceptor size scales with the kitchen. A 25 gallon-per-minute, 50 pound trap covers delis and coffee shops, and a 1,000 gallon interceptor covers limited- and full-service restaurants. Buffets and cafeterias need 1,500 gallons, and schools, hospitals and prisons need 2,000 gallons. The same document warns that some restaurants in its heavier classes "will need to consider a 30 day pumping frequency or a 60 day pumping frequency to meet the 25 Percent Rule requirement."

The plumbing code sizes by flow, not gallons. According to the International Plumbing Code's grease interceptor capacity table (2024 edition, as published on up.codes), a 20 gallon-per-minute interceptor pairs with 40 pounds of grease retention and a 100 gpm unit with 200 pounds. Above 100 gpm, the retention requirement is double the flow rate. A small under-sink trap rated for 40 pounds of grease reaches its limit far sooner than a 1,000 gallon tank, which is why Charlotte Water's grease trap policy (charlottenc.gov) asks for under-sink traps monthly and outside traps quarterly.

The practical rule: measure before you schedule. Have the hauler record FOG depth and solids depth on the manifest at every pump-out. If the trap is consistently near the trigger at 90 days, tighten the interval. If it is at 10 percent, you can make the case to your utility for the interval you are already on. Related reading on how kitchens handle the other recurring fire and sanitation contract: our hood cleaning contract prices dataset.

What a pump-out costs

Pump-out pricing is rarely published, so the best public data is government bid tabulations, where several haulers price the same tank on the same day. Vendor price guides fill in the small-trap end. The table labels which is which.

Two things stand out. First, the spread between haulers on identical scope is large. According to Dallas County Purchasing's 2009 bid tabulation for grease and sand trap services (dallascounty.org), the same 1,000 gallon kitchen trap drew bids of $190, $248 and $400, and the same 3,000 gallon trap drew $1,004, $1,200 and $2,000. Getting three quotes is not paranoia; it is the difference between paying once and paying twice. Second, tank size drives price roughly in step with volume. According to Lubbock County's 2022 pumping award (lubbockcounty.gov), a 2,000 gallon tank cost $630 against $320 for a 1,000 gallon tank, roughly double for double the volume.

The vendor guides are useful for the small indoor traps that public bids rarely cover. According to Grease Cycle's pumping cost guide (grease-cycle.com), a 30 to 200 gallon indoor trap runs $125 to $180 on a service program and $190 to $240 as a one-off. The scheduled contract that keeps you compliant is also the cheaper way to buy the service. Treat all three vendor ranges as advertising, not benchmarks; they are the hauler's own numbers.

What to log and photograph

Every city in the table that says anything about records wants the hauler manifest kept on site, and the retention period is not consistent. Dallas, Austin, Phoenix and Charlotte require three years. Houston requires five. Bloomington wants the cleaning receipt copied to the utility within 14 days of each cleaning. According to Austin Water's grease trap maintenance page (austintexas.gov), "failure to meet any one of these maintenance or documentation requirements is a separate violation," so a missing manifest is a fine even when the trap itself is clean.

For multi-site operators the photos matter as much as the paper. A manifest proves a truck came. A photo proves what the trap looked like when it did, and whether the lid, gasket and baffles went back in place afterward. Treat the grease trap like any other property-condition item on a site walk: the same discipline that catches a cracked hood filter or a missing fire extinguisher tag catches a trap that has not actually been scraped. If your team already captures site photos on a schedule, RapidEye can review them and flag the trap that looks the same before and after its "service." Our guide to smart glasses for restaurant inspections covers how some kitchens capture that walk hands-free, and our restaurant health permit fees and fines by city page covers the other inspector who wants to see your paperwork.

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