Grease Trap Cleaning Frequency: How Often to Clean Yours

Most commercial kitchens should clean a grease trap every one to three months. That is only a starting point. The real rule is to clean it before grease and solids fill 25% of its liquid depth, and for a small indoor trap in a busy kitchen that can mean every week or two. Your city’s ordinance sets the legal minimum, and your own cooking volume decides whether that minimum is enough.

Below we explain how the 25% rule works, what schedules cities commonly set for each type of device, how to work out your own interval, and what inspectors check besides the trap itself.

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TL;DR

Clean a trap when floating grease plus settled solids reach 25% of its total liquid depth, or on your local ordinance’s schedule, whichever comes first.
Small indoor traps often need service every one to four weeks. Large outdoor interceptors are commonly set at about every 90 days.
A 90-day schedule is a legal floor, not a recommendation. Heavy frying usually fills a trap sooner.
Keep cleaning logs and hauler manifests on site. Missing paperwork can count as a violation even when the trap is clean.
Additives do not replace pumping. Use a licensed waste hauler for the pump-out.

The 25% rule: the limit that overrides the calendar
Typical cleaning schedules by type of device
Why 90 days is a floor, not a goal
How to set your own cleaning interval
The paperwork inspectors actually check
Who is allowed to clean the trap
Do additives let you clean less often?
Our perspective on grease trap schedules
When the problem is beyond the trap
FAQ
Sources

The 25% rule: the limit that overrides the calendar

A grease trap works by slowing wastewater so fats, oils and grease (FOG) float to the top while food solids settle to the bottom. Water in the middle flows on to the sewer. Once the two layers take up too much of the device, it stops separating and grease passes through.

The standard measure is the 25% rule. Under the Texas Commission on Environmental Quality’s model grease ordinance, a trap must be cleaned when the combined depth of the floating grease layer and the settled solids reaches 25% of the device’s total liquid depth. Utilities elsewhere use the same threshold. The Des Moines Metropolitan Wastewater Reclamation Authority FAQ says it applies to both grease interceptors and grease traps.

The point most owners miss: the 25% rule is a performance limit, not a maintenance schedule. If your trap hits 25% on day 40 and your schedule says day 90, the trap is overdue on day 40. The calendar does not protect you.

How to check the 25% level

Your hauler or the manufacturer’s manual will show the trap’s liquid depth. Measure the depth of the grease layer from the surface, and the depth of solids from the bottom, then add them. If the total is a quarter or more of the liquid depth, it is time to pump. Do this on a fixed day each week at first so you build a real picture of how fast your kitchen fills the trap.

Typical cleaning schedules by type of device

There is no federal rule that sets one number for every kitchen. Cities and sewer districts write their own, and they differ by device size.

Device	Typical location	Common schedule
Small hydromechanical grease trap (about 20 to 75 gallons)	Under a sink or on the kitchen floor	Every 2 weeks to monthly
Large gravity grease interceptor (hundreds to thousands of gallons)	Buried outside the building	About every 90 days
Automatic grease removal device	Indoors, with electromechanical skimmer	Device cleans itself daily, with staff emptying and maintenance per the manufacturer and ordinance

The figures behind the table come from local programs. Lawrence, Kansas is one example of a city that uses roughly 90-day intervals for large outdoor interceptors and monthly or even bi-weekly intervals for smaller indoor traps, depending on cooking volume. Nashville’s Metro Water cleaning log lists a recommended interval of every two weeks for an undersink trap, which it describes as usually 20 to 50 gallons.

The size definitions matter too. Los Angeles County’s restaurant pretreatment guidelines define a grease trap as a small, single-compartment device of 25 to 75 gallons. A grease interceptor is a larger unit with two or more compartments. The smaller the device, the less room it has, and the faster it fills.

If you are not sure which one you have, our guide What Is a Grease Trap? explains the difference and how each is sized.

Why the same kitchen can need different intervals

Two restaurants with the same trap can have very different fill rates. These are the factors that move the number:

Menu. Deep frying, fried chicken, bacon, cheese-heavy dishes and anything cooked in oil put far more FOG in the wastewater than a salad and sandwich counter.
Covers per day. More dishes washed means more grease sent down the drain.
Trap size relative to the kitchen. An undersized trap fills quickly no matter how careful the staff are.
Scraping habits. Plates scraped into the trash before washing keep solids out of the trap. Plates rinsed straight into the sink do not.
Dishwasher and sink connections. Hot water can carry grease past an undersized trap before it has cooled enough to separate.
Seasonal swings. A patio restaurant, a campus cafeteria or a stadium concession may fill a trap in a few days during peak weeks.

Why 90 days is a floor, not a goal

Many ordinances set a quarterly maximum. According to industry guidance on grease interceptors, that 90-day figure works as a minimum safety floor rather than a recommendation for good performance, and high-volume kitchens that fry a lot can fill their traps well before it. Relying on the generic number without checking actual buildup is how kitchens end up with odors, blocked lines and emergency calls.

The cost of getting it wrong is not just the trap. When grease gets past a full trap it hardens in your building’s drain line or in the city sewer. You then face a drain stoppage, possible fines, and in a bad case liability for a sewer overflow. Recognizing early signs helps: slow floor drains, gurgling, and a sour smell from the kitchen. Our article on signs of sewer line problems covers what a backed-up line looks like further down the pipe.

How to set your own cleaning interval

You can build a schedule from your own data in about a month.

Find your local requirement. Look up your city or county FOG program, or your sewer district’s ordinance. Note the maximum interval and whether it applies to traps, interceptors or both.
Start at the shortest likely interval. For a small indoor trap, begin with every two weeks. For a large interceptor, begin with the ordinance’s maximum.
Measure weekly. Record the grease and solids depth against total liquid depth each week. Practitioners recommend weekly or bi-weekly checks to work out a site-specific accumulation rate, according to the Lawrence, Kansas city FOG program.
Project the date of 25%. If the trap reaches about 10% after one week, you will hit 25% in roughly two and a half weeks. Schedule service a little before that.
Adjust for menu and season. Re-measure when you change the menu, add a fryer or enter your busy season.
Never go longer than the ordinance allows. Even if your trap fills slowly, the legal maximum still applies.

Write the result down. A schedule you can show an inspector is worth more than a good guess.

The paperwork inspectors actually check

Cleaning the trap is half the job. According to Kitchen Management Authority’s overview of grease trap management, citing Water Environment Federation and local FOG program practice, many failures are really breakdowns in documentation. If logs are missing or incomplete, the business can be considered out of compliance whatever the trap looks like.

What to keep on site:

A maintenance log with the date, the grease and solids level and who serviced the device.
Waste manifests from your hauler for every pump-out.
Records of any repairs, baffle or lid replacements.

How long to keep them depends on your jurisdiction. The Des Moines area authority advises keeping hauler manifests on site for at least three years. Check your own city’s number.

Who is allowed to clean the trap

There is no single federal license for grease trap cleaning. Businesses follow local, city or county ordinances. In many places that means using a state-licensed waste hauler and keeping manifests for inspection, as in Texas, where the TCEQ’s guidance on grease trap waste covers transporters and disposal. The TCEQ model ordinance also says each trap should be fully evacuated, not just skimmed, unless the vacuum truck cannot hold the volume.

Some jurisdictions allow staff to clean small indoor units themselves. It carries real liability. The James City County, Virginia FOG policy is one example of a local policy that governs these devices and how they must be maintained. If you clean in-house you still need rigorous records, and pouring grease into other drains or the trash can cause the very blockages and fines you were trying to avoid. For commercial kitchens, a licensed hauler is the most reliable path.

Who is allowed to clean the trap — overview diagram

Do additives let you clean less often?

No. Regional water authorities warn that enzyme and chemical additives often only liquefy grease for a while. The grease can then slip past the trap and harden farther down in the sewer, creating bigger blockages and putting the business at risk for overflow damages. The City of Joliet’s FOG program explains how traps and interceptors have to be properly sized, installed and maintained to work. Additives can sit alongside regular pumping if your local program permits them. They are not a substitute for it.

Our perspective on grease trap schedules

We work on commercial plumbing in Burbank, and the pattern we see in kitchens is consistent: owners hear “every 90 days” and treat it as a promise. It is a ceiling set by a city, not a measurement of your kitchen.

Our advice is simple. Measure first, then schedule. A few minutes each week gives you the accumulation rate, and that number is better than any rule of thumb. When the trap is the right size and cleaned on a schedule that matches how you cook, the drain lines behind it stay clear and inspections are routine.

When a kitchen keeps filling its trap far faster than expected, the cause is often not discipline but design: an undersized trap, a poorly placed fixture or a drain line that has built up grease downstream. Those are plumbing problems, and they are cheaper to fix on a planned visit than during a Friday-night backup. Our guide to commercial kitchen plumbing specs and checklist covers the layout points we look at.

— Serghei

When the problem is beyond the trap

If your trap is cleaned on time but drains still run slow, grease may already have coated the pipes behind it. We handle commercial drain cleaning and hydro jetting, which clears built-up grease from the line itself, and can inspect your sewer line when you suspect a deeper blockage. For ongoing facility work, see our commercial plumbing services or request a free quote. We are licensed and insured. For the pump-out of the trap itself, use a licensed waste hauler as your local rules require. Our commercial drain cleaning guide explains how the two fit together.

FAQ

How often do grease traps need cleaning?

A common guideline is every one to three months, but the right interval depends on trap size and cooking volume. Small indoor traps in busy kitchens are often serviced every two weeks to monthly. Whatever the schedule, clean the trap as soon as grease and solids reach 25% of its liquid depth.

How often should a grease trap be emptied?

Empty it on the shorter of two dates: your ordinance’s required interval or the date the 25% limit is reached. Large outdoor interceptors are commonly set at about every 90 days. Smaller indoor units are emptied far more often.

Do I need a license to clean grease traps?

There is no single federal license. Rules come from your city, county or state, and many places require a state-licensed waste hauler plus manifests kept on site. Check with your local FOG or pretreatment program before hiring anyone or cleaning in-house.

What happens if I miss a cleaning?

You risk a backup, odors and an inspection finding. A trap that is past 25% is overdue even if your calendar says otherwise, and missing logs can count against you on their own. Fines and liability for sewer overflows depend on your local ordinance.