Pumping Frequency & the 25/50 Rule
The 25/50 rule is the single most important compliance threshold in FOG management. Exceed it and you fail inspection. This guide explains what the rule means, how it's measured, and how pumping frequency is set across US cities.
What Is the 25 Percent Rule?
The 25 percent rule is a compliance threshold that dates back to U.S. Environmental Protection Agency pretreatment guidance in the 1990s. It states:
A grease trap or interceptor must be cleaned out before the combined depth of floating fats, oils, and grease (FOG) and settled solids exceeds 25 percent of the total operating liquid depth of the unit.
The rule recognizes a physical reality about how traps work: when FOG and sludge layers together occupy more than a quarter of the trap, the middle "clean water" layer gets pushed so close to the outlet pipe that grease starts escaping to the sewer. Once that happens, the trap is effectively bypassed — FOG accumulates in sewer mains, causing fatbergs and sanitary sewer overflows (SSOs).
What Is the 50 Percent Rule?
Many cities pair the 25 percent FOG limit with a separate 50 percent limit on settled sludge. Together they are called the 25/50 rule. Under this variant:
- FOG layer (floating grease at top): must not exceed 25% of total liquid depth.
- Sludge layer (settled solids at bottom): must not exceed 50% of total liquid depth.
Why separate thresholds? Solids accumulate differently from FOG. A high-volume dishwashing operation might generate tons of food particles without much grease, while a fry-heavy kitchen is the opposite. Separate thresholds ensure both failure modes trigger a pump-out.
How Inspectors Measure the Rule
Local wastewater inspectors — sometimes called FOG inspectors, pretreatment inspectors, or sewer compliance officers — perform both scheduled and surprise inspections. They use one of three tools:
- Sludge judge. A clear polycarbonate tube, typically 5 to 10 feet long, with a check valve at the bottom. Lowered into the trap, it captures a vertical column of the liquid, clearly showing the FOG, water, and sludge layers. Inspectors measure each layer's depth in inches.
- Bar-and-paste dipstick. A wooden or metal rod coated with water-finding paste. The paste changes color where it touches water, revealing the depth of the FOG cap above.
- Visual inspection through access ports. For smaller traps, removing the cover and using a flashlight and ruler to measure layers directly.
The inspector calculates: (FOG depth + sludge depth) ÷ total liquid depth. If the result
exceeds 0.25 (25%), the trap fails inspection and must be pumped immediately.
Pumping Frequency vs. the 25/50 Rule
Pumping frequency and the 25/50 rule are two different compliance mechanisms. Both apply simultaneously in most cities:
- Scheduled pumping frequency is the maximum time allowed between pump-outs, regardless of how full the trap is. A typical ordinance requires pumping "every 90 days or when the 25 percent threshold is reached, whichever comes first."
- The 25/50 rule is a hard ceiling that overrides the schedule. Even if your 90-day pump-out isn't due for three weeks, if the trap hits 25 percent today, you must pump today.
Pumping Frequencies by Jurisdiction
Pumping frequency varies significantly across US cities. Based on our database of 246 cities:
| Frequency | Typical Jurisdictions | Who It Applies To |
|---|---|---|
| Every 30 days | Houston, parts of Florida, Los Angeles County (high-volume tier) | High-volume full-service restaurants, commissaries, institutional kitchens |
| Every 60 days | Several Texas and California cities | Mid-tier restaurants and food service |
| Every 90 days | Most US cities (default) | Standard full-service restaurants |
| Every 180 days | Lower-volume jurisdictions, some Midwestern cities | Cafes, delis, low-FOG establishments |
| Annually | Some jurisdictions with variance programs | Coffee shops, bakeries, ice cream parlors with documented low FOG |
| On the 25/50 rule only | A minority of cities | All establishments — no time-based schedule |
Find your city's specific frequency in our city regulations database.
What Happens if You Exceed 25 Percent
Consequences of a failed inspection escalate with repeat violations:
- Notice of Violation (NOV). First offense typically triggers a written NOV with a deadline (often 5 to 30 days) to bring the trap into compliance.
- Fines. Range from $100 to $10,000+ per day depending on jurisdiction. Los Angeles County can fine up to $25,000 per day under the federal Clean Water Act for severe violations.
- Emergency pump-out mandate. You're given 24 to 72 hours to pump.
- Increased inspection frequency. Violators often move to a "watch list" with monthly inspections for 6 to 12 months.
- Permit revocation or closure. Repeat non-compliance can trigger revocation of your FOG permit or, combined with health code issues, forced closure of the establishment.
How to Stay Under 25 Percent
- Schedule pump-outs 25 to 30 percent earlier than your "deadline." If you're on a 90-day schedule, book the hauler for day 65 to 70 so you have a buffer.
- Measure weekly. A clear sludge judge is a $40 to $80 one-time purchase. Run it yourself every Monday and keep a log.
- Track menu changes. Adding a fryer, new prep equipment, or a higher seat count increases FOG load. Re-verify with our sizing calculator.
- Train staff on source control. Scraping plates into trash (not sinks), wiping pans before washing, and using strainers on every drain reduce the volume of FOG reaching the trap.
- Keep pumping manifests on site. Inspectors ask for the last 3 manifests. Missing paperwork is itself a violation in most cities.
Check Your City's Exact Pumping Rule
We track pumping frequency, permit fees, and fines for 246 US cities.
Find Your CityFrequently Asked Questions
What is the 25 percent rule for grease traps?
The 25 percent rule requires restaurants to pump out their grease trap before the combined fats, oils, grease (FOG), and settled solids reach 25 percent of the trap's total liquid depth. Most US cities enforce this rule through periodic inspections where an inspector uses a dipstick or sludge judge to measure the FOG and sludge layers.
What is the 50 percent rule?
Some jurisdictions pair the 25 percent FOG rule with a 50 percent solids rule — settled sludge at the bottom of the trap cannot exceed 50 percent of the total liquid depth before pumping is required. Together these are often called the "25/50 rule."
How often should I pump my grease trap?
Most US cities require grease trap pumping every 90 days. More strict jurisdictions require monthly pumping (every 30 days) for high-volume restaurants, and some allow annual pumping for low-FOG establishments. Pumping frequency depends on your city's ordinance, not just the 25/50 rule.
Who measures the 25 percent threshold?
Licensed grease haulers measure the FOG and solids depth at every pump-out using a clear sampling tube or sludge judge. City inspectors also measure it during scheduled or surprise inspections. You can measure it yourself with an inexpensive clear poly sludge judge purchased from a plumbing supplier.
What happens if my grease trap exceeds 25 percent?
If an inspector finds your trap over the 25 percent threshold, you will typically receive a notice of violation, be required to pump immediately, and face fines ranging from a few hundred dollars to thousands depending on your city. Repeat violations can result in permit revocation or closure.
Does the 25 percent rule apply to all grease traps?
The rule originated in EPA pretreatment guidance and is adopted by most US cities, but not all. Our database of 246 US cities tracks which jurisdictions explicitly enforce the rule — check your specific city for the applicable ordinance.
Related Guides
How Grease Traps Work
Full explainer of FOG separation physics, components, and code.
Grease Trap FAQ
20+ answers to common FOG compliance questions.
Disclaimer: Regulations vary by jurisdiction and change frequently. Always verify current requirements with your local wastewater authority or plumbing inspector. Last updated: .