The working answer on how often to clean a grease trap is before it reaches one quarter full of grease and solids, which for most restaurants lands somewhere between every month and every three months. Let it run past that and you are risking a grease line backup during service, a failed health inspection over your records, and in a bad case a closure order while the kitchen sits idle.
The 25 percent figure is the rule of thumb the trade and most authorities work from. Your actual interval is set by your trap size, your volume and what you cook, and the exact requirement is set by your local health authority and sewer program. Here is how to work out yours.
What the 25 percent rule actually means
A grease trap works by slowing water down enough for fats, oils and grease to float and solids to sink, so only the middle layer leaves for the sewer. It needs empty volume to do that.
Once a quarter of the trap’s capacity is taken up by the grease cap on top and the solids layer on the bottom, the water moving through has less room and less time to separate. Grease starts leaving with the outflow. It cools in your branch line and hardens on the pipe wall, which is where the actual blockage forms weeks later.
That is why a trap can look like it is “working” right up to the morning nothing drains. The trap did not fail that day. It stopped separating properly a month earlier and has been coating your waste line ever since.
Measure the trap rather than guessing. A dipstick reading of the grease cap and the solids layer against total depth tells you where you are. Log the reading each time and the interval works itself out after two or three cycles.
What drives your interval
Two kitchens with the same trap can need very different schedules. These are the factors that actually move it:
| Factor | Pushes cleaning more often | Pushes cleaning less often |
|---|---|---|
| Trap capacity | Small under-sink unit, 20 to 50 gallons | In-ground interceptor, 750 gallons and up |
| Covers per day | High volume, long service hours | Low volume, limited hours |
| Cuisine | Fried food, heavy sauces, butter and dairy | Salads, sushi, cold prep, coffee |
| Equipment connected | Wok range, fryers, tilt skillet, dish machine | Prep sink and hand sink only |
| Kitchen practice | Grease poured to drain, no dry-wiping | Scrape and dry-wipe before washing |
| Season | Summer, when heat keeps grease liquid longer downstream | Cooler months |
The last row surprises people. Warm weather does not fill a trap faster. It changes where the grease solidifies, because it stays liquid further along the line before it cools and sets. A restaurant that gets through winter without a backup can still block a lateral in August with the same habits.
Field note
A café kitchen with a small under-sink trap was on a quarterly schedule that worked fine for two years. They added a fryer and a second dish shift, kept the same schedule, and blocked the branch line eight weeks later during a Saturday lunch. The trap was not undersized for the building. It was undersized for the menu they were now running. Any time equipment or service hours change, the interval has to be re-checked, not inherited.
Under-sink traps and in-ground interceptors are different jobs
The words get used interchangeably, and they are not the same problem.
A hydromechanical grease trap, usually under a three-compartment sink or nearby on the floor, holds tens of gallons. It fills quickly, it is cleaned often, and in a busy kitchen that can mean monthly or more.
A gravity grease interceptor, usually a concrete tank outside in the parking area, holds hundreds or thousands of gallons. It is pumped by a licensed hauler, less often, and the waste is manifested and disposed of at a permitted facility.
Most restaurants have one or the other. Some have both, and the small one still needs attention on its own cycle even when the big one was pumped recently.
What your local authority actually requires
Here is the part that generic advice gets wrong: there is no single national interval, and there is often not a single local one either.
Two different bodies usually have a say. The county health department inspects your facility and looks at grease trap condition and your records as part of the food facility inspection. The sewer or wastewater authority runs the fats, oils and grease program that governs what you discharge, and that is usually where a required cleaning frequency, a manifest requirement and a record retention period come from.
For a Sacramento restaurant, that means checking with Sacramento County Environmental Management on the food facility side, and with your sewer provider, commonly the City of Sacramento Department of Utilities for city addresses, on the discharge side. Requirements can also be written into your own facility permit, which overrides the general guidance.
Current as of July 2026. Confirm your required interval, manifest format and record retention period with both authorities, because a schedule that satisfies one does not automatically satisfy the other.
Records are what fail inspections, not grease
A trap that is slightly overdue is a conversation. A trap with no paperwork is a finding.
Keep these on site, not in an accountant’s inbox:
- Service manifests from every cleaning, with date, hauler, volume removed and disposal site
- The hauler’s licence or permit details, since waste has to go to a permitted facility
- Your own log of dipstick readings between services
- Any repair records for baffles, lids or flow control fittings
- The trap’s size and location, which sounds obvious until an inspector asks and nobody knows
Retention periods vary by jurisdiction, and a common expectation is two to three years of history available on request. Confirm yours. Keeping more is cheap.
Frequency and cost, by trap type
Ranges, not prices. Anyone quoting a firm number before seeing the trap, the access and the volume is guessing.
| Trap type and size | Typical interval | What moves the cost |
|---|---|---|
| Under-sink hydromechanical, 20 to 50 gal | Every 2 to 6 weeks in a busy kitchen | Access under a fitted counter, disposal volume |
| Floor-mounted hydromechanical, 50 to 100 gal | Monthly to quarterly | Whether the kitchen must be closed to work |
| Small in-ground interceptor, 500 to 1,000 gal | Quarterly, sometimes more often | Truck access, distance to the disposal site |
| Large in-ground interceptor, 1,500 gal and up | Quarterly to twice a year | Depth, lid condition, volume pumped |
| Any trap, out-of-hours service | Same interval, higher rate | Night or early morning scheduling |
Two things reliably cost more than the cleaning itself: an emergency call when the line blocks during service, and a jetting job on a lateral that has been coated for months. Both are avoidable with a calendar.
Signs your interval is too long
Run through this list monthly. Any two together means move the schedule up, not wait for the next scheduled service.
- Slow floor sink or floor drain near the dish or prep area during normal operation
- Gurgling from a floor drain when the dish machine discharges
- Odour near the trap or the floor sinks that cleaning products do not fix
- A visible grease cap more than a quarter of the trap depth at your dipstick check
- Grease at the outlet side of the trap, which means it is carrying over
- A backup that cleared “on its own”, which usually means it moved rather than cleared
- The hauler is removing noticeably more each visit than the visit before
What a proper cleaning includes
This is not a bucket-and-shovel job, and it is not a job for kitchen staff. Confined space, hot fats and waste handling rules all apply, and improperly disposed grease waste is its own violation.
A service visit worth paying for includes pumping the full contents rather than skimming the top layer, scraping the walls and baffles, checking the baffles and flow control fitting are intact and in place, inspecting the lid and gasket, and leaving you a manifest the same day.
Skimming the surface and leaving the solids is the most common shortcut. The trap looks empty and fills again in half the time.
What about additives and enzyme treatments
Operators ask about this constantly, usually because a supplier has offered a monthly dosing product as a way to stretch the interval.
Be careful. Products that emulsify or dissolve grease do not remove it from the system, they move it further down the line, where it cools and sets somewhere less convenient than your trap. Some jurisdictions restrict or prohibit them in FOG programmes for exactly that reason, since the grease still reaches the sewer.
Biological products that digest fats behave differently from chemical emulsifiers, and some sewer authorities permit them as a supplement. None of them replace pumping, and none of them empty the solids layer at the bottom of the trap.
Two rules. Check with your sewer provider before using any additive, because a product that is fine in one jurisdiction can be a violation in another. And never treat an additive as a reason to extend the interval, because the inspector measures the trap, not the dosing schedule.
Before your next health inspection
Ten minutes with this list is the cheapest inspection prep you will do:
- Pull the last three manifests and confirm the dates match your stated schedule
- Take a dipstick reading and write it in the log with today’s date
- Open the lid and look at the baffles, since a broken baffle means the trap is not separating whatever the schedule says
- Check the flow control fitting is present on the inlet side
- Confirm every fixture that should drain to the trap actually does, especially anything added during a remodel
- Check the floor sinks and air gaps at the dish machine and ice machine, which is where inspectors look next
- Put the manifest file somewhere the manager on shift can find it, not in the office of someone who is off that day
There is a fuller list of what inspectors open first in what health inspectors check on a restaurant’s plumbing.
When to bring in a commercial plumber
A hauler pumps the trap. A plumber is the call when the problem is the plumbing around it:
- The trap is clean and the line still drains slowly, which points to grease already set in the branch or the lateral
- A baffle, lid, flow control fitting or trap body is damaged
- You are adding a fryer, a wok range or a dish machine and need to know whether the existing trap and lines can carry it
- The trap is undersized for the menu you now run and you need a sizing recommendation before a plan check
- You need the waste line jetted and camera checked rather than rodded
Put it on the calendar, not the to-do list
The restaurants that never have a grease emergency are not lucky, and they do not have better traps. They have a recurring date, a dipstick log, and a manifest file the shift manager can find in under a minute.
If you want the schedule set by measurement rather than guesswork, we service traps and interceptors and jet the lines behind them for kitchens across the Sacramento area. See commercial grease trap services, or call [PHONE] with your trap size and your menu and we will tell you what interval it actually needs.