Most restaurants need their grease trap cleaned every one to three months, and small under-sink traps in busy kitchens often need it monthly or even more frequently. The controlling standard in most jurisdictions is not a fixed calendar interval but a condition: pump before accumulated grease and solids fill about 25% of the trap's depth, or sooner if your local wastewater authority sets a stricter rule.
The 25% rule sets your floor, your kitchen sets your pace
The widely used "25% rule" says a grease trap must be serviced once the combined floating grease layer and settled solids occupy one quarter of the trap's liquid depth. Beyond that point the trap loses much of its separation capacity, and grease starts passing through to the sewer. This is a common local standard written into many municipal FOG (fats, oils, and grease) ordinances — it is not a federal law, and your local wastewater authority's rules are what actually govern your facility. Some cities instead mandate minimum pump-out intervals (for example, every 90 days) regardless of measured accumulation, and some require both. We break the details down in the 25 percent grease trap rule.
The regulatory backdrop is the U.S. EPA's national pretreatment program, which requires municipalities to control what nondomestic sources discharge into sewers. Grease is a leading cause of sewer blockages and sanitary sewer overflows, so local FOG programs — permitted haulers, pumping requirements, record-keeping — are how cities meet that obligation. Your first stop for the binding numbers is always the local sewer authority, not a national rule of thumb.
Typical schedules by trap type and kitchen volume
As practical starting points, before you adjust to your own measurements:
Small indoor traps (20–100 gallons). These fill fast. A busy full-service kitchen may hit 25% capacity in two to four weeks. Many operators put small traps on a monthly cleaning cycle and check them more often during peak season.
Mid-size traps and hydromechanical units (100–750 gallons). Every one to two months is a common cadence for moderate-volume kitchens.
Large outdoor gravity interceptors (750–2,000+ gallons). Quarterly pumping is a frequent baseline, and many jurisdictions codify 90 days as the maximum interval. High-volume operations — fried-food concepts, high-cover restaurants, commissaries — often need these pumped every one to two months. See grease interceptor pumping for how full-service pump-outs work.
Low-grease operations. A coffee shop or a kitchen with minimal frying may legitimately go longer, but only if the local authority allows a variance and your measured accumulation supports it. Get any extended interval approved in writing.
How to find your actual interval
Rather than guessing, measure. When your hauler services the trap, ask how full it was — a good hauler will note the grease and solids depth on the service record. If the trap was at 25% at 60 days, a 60-day schedule is about right; if it was at 25% in 30 days, tighten the schedule. Some operators or their haulers use a dipstick check (a clear tube or measuring rod through the grease and solids layers) between services to track accumulation.
Then re-check whenever your operation changes. A new fryer, an expanded menu, higher covers, a switch from disposable to washed dishware, or a new tenant sharing the interceptor can all shorten the interval materially.
Signs you have waited too long
- Slow-draining sinks and floor drains, or gurgling in kitchen plumbing
- Grease odors near drains, the trap, or the dumpster area
- Visible grease in the trap's outlet chamber or downstream cleanout
- A backup — the most expensive way to learn your schedule was wrong
By the time symptoms appear, grease has usually already escaped into your building's drain lines or the city sewer. That can mean an emergency pump-out at premium rates, a jetting bill for your own lines, and a violation notice if the city traces a blockage or discharge exceedance to your connection.
Cleaning more often is usually cheaper overall
Each additional pump-out costs money, but neglect costs more: hardened grease that takes extra labor to remove, plumbing service calls, surcharges for high-strength discharges, fines, and in bad cases forced closure while a backup is cleaned up. Pricing and the trade-offs are covered in grease trap cleaning cost.
You can also stretch intervals honestly with kitchen practices: dry-wipe cookware before washing, scrape plates into the trash, keep fryer oil out of drains entirely (used cooking oil goes to a separate collection container, typically hauled at low or no cost), and train staff not to pour anything greasy down the sink. Enzyme and bacteria additives are heavily marketed, but many wastewater authorities prohibit or discourage additives that merely liquefy grease and push it downstream — check your local FOG rules before relying on them, and never use additives as a substitute for pumping.
Keep records on the schedule, not just the service
Most FOG programs require you to keep manifests or service records on site — commonly for around three years, though the retention period is set locally — showing each cleaning date, the hauler, the volume removed, and the disposal destination. Inspectors use these records to verify your interval. What a compliant record looks like is covered in FOG manifest requirements.
Choosing and verifying a hauler
Use a hauler your local wastewater authority permits or registers — many cities publish the list, and using an unlisted hauler can itself be a violation. Before hiring, confirm the permit is current, ask which approved facility receives the waste, and require a manifest or service record for every visit. Put your required interval in the service agreement so the schedule runs automatically. A directory like ours helps you find and compare local grease trap service companies from source-backed public records, but no directory certifies a hauler — verification always runs through your wastewater authority's own lists.