The "25% rule" is a widely used maintenance benchmark: when the combined layer of fats, oils, grease (FOG), and settled solids reaches 25% of a grease trap's total liquid depth, the trap should be pumped and cleaned. It is not a federal law — it's a standard that many municipal FOG (fats, oils, and grease) programs and wastewater authorities have adopted locally, so the specific threshold and enforcement mechanism in your jurisdiction depend on your local ordinance.
Where the 25% Rule Comes From
Grease traps and interceptors work by slowing wastewater flow so FOG floats to the top and solids settle to the bottom, leaving cleaner water to pass through to the sewer. As FOG and solids accumulate, the effective liquid depth and retention time shrink, and the device becomes less effective at separating grease before it reaches municipal pipes. The 25% threshold emerged as a practical industry rule of thumb — pump before capacity is meaningfully compromised, not after the trap is already failing.
The U.S. EPA's National Pretreatment Program gives municipalities authority to set local limits and require pretreatment (including grease traps and interceptors) for restaurants and other high-FOG dischargers under the national pretreatment program. EPA does not itself mandate a 25% pump-out threshold — that detail is left to local control authorities, which is why cities and counties vary in how they define and enforce it.
How the 25% Rule Is Measured
A technician measures three layers in the trap: the FOG cap on top, the wastewater in the middle, and settled solids on the bottom. The combined depth of FOG plus solids is compared to the total liquid depth of the trap. Once that combined layer hits roughly a quarter of total depth, it's time to pump — regardless of how much time has passed since the last cleaning. This is different from a strict calendar-based schedule (e.g., pump every 90 days) because grease accumulation varies with cooking volume, menu, and kitchen habits.
Why Local Ordinances Vary
Because FOG discharge is regulated at the local level under EPA's pretreatment program framework, municipalities write their own ordinances covering:
- The exact percentage threshold — most use 25%, but some local programs specify different figures or a maximum time interval instead (or in addition).
- Minimum pumping frequency, regardless of fill level, often ranging from monthly to quarterly for active food service establishments.
- Manifest and reporting requirements — many FOG programs require haulers to file a trip ticket or manifest documenting each pump-out.
- Permitted hauler lists — many wastewater authorities maintain a list of haulers authorized to service grease traps in their service area.
Because of this variation, the only way to know the exact rule that applies to a specific restaurant or facility is to check with the local wastewater authority or FOG program administrator.
What Happens If You Ignore the 25% Threshold
Letting a trap exceed the 25% fill level reduces its ability to separate grease before wastewater leaves the property. Over time this can lead to grease building up in the property's lateral line and the municipal sewer main downstream, increasing the risk of blockages and sanitary sewer overflows. Many local programs cite excessive FOG discharge as a leading cause of preventable sewer backups, which is part of why enforcement (inspections, fines, and permit conditions) tends to be strictest for high-volume food service establishments.
Typical Costs Tied to 25% Rule Compliance
Grease trap pumping costs vary by trap size, grease volume, and local disposal fees, but as a general range, most small to mid-size interceptor pump-outs run from roughly $150 to $500 per service, with larger in-ground interceptors costing more. Facilities that let FOG accumulate past 25% before calling for service sometimes pay more per visit because there's more material to remove and dispose of. Sticking to a proactive schedule based on measured fill level (rather than waiting for a problem) tends to keep per-visit costs more predictable.
How to Choose and Verify a Grease Trap Service Company
Before hiring a grease trap service company, verify the following:
- Confirm they're on your local permitted hauler list. Many municipal FOG programs publish a list of haulers authorized to collect and transport grease trap waste within their jurisdiction — ask the company directly or check with your local wastewater authority.
- Ask how they measure fill level. A reputable provider should explain how they determine whether your trap has reached the 25% threshold (or whatever standard your local ordinance uses) rather than just pumping on a fixed schedule regardless of actual accumulation.
- Request a manifest or trip ticket documenting the pump-out, the volume removed, and the disposal facility used — many local programs require this for compliance recordkeeping.
- Confirm proper disposal. Ask where the waste is taken and whether the disposal facility is permitted to accept FOG waste.
This directory is an independent, source-backed listing of public records about grease trap service providers — it does not certify, license, or endorse any company. Always verify permitting and compliance status directly with your local wastewater authority or FOG program before hiring.
FAQs
Is the 25% rule federal law? No. It's a common local/industry standard adopted by many municipal FOG programs, but it is not codified in federal law. Your local wastewater authority's ordinance is the governing rule.
What if my city doesn't use the 25% rule? Some jurisdictions use a different percentage, a maximum time interval, or both. Check your local FOG program's requirements or ask your grease trap service company what standard applies in your area.
Can I measure the 25% level myself? Some facility managers monitor fill level with a dipstick between service visits, but professional technicians are trained to measure it accurately and are typically required to log results on a manifest for compliance purposes.