The Short Answer
Clean a grease trap or interceptor before the combined layer of floating grease and settled solids reaches 25 percent of its liquid capacity. Many California cities also set a minimum schedule, such as a full pump-out at least every 90 days or every six months. The rule that applies to you comes from your local sewer agency, so ask them in writing.
A schedule alone is not enough. Agencies often expect a maintenance log, a licensed hauler, and receipts you can show an inspector. This article is general information, not a legal opinion on your permit.
How Agencies Set The Schedule
| Example | Rule | Takeaway |
|---|---|---|
| City of Folsom, California | Clean when grease and solids reach 25 percent of volume. Pump out completely at least once every six months. | A floor schedule plus the 25 percent trigger. |
| City of Brentwood, California | Gravity grease interceptors are pumped at a minimum of every 90 days, or sooner if they exceed 25 percent. | A shorter minimum for large interceptors. |
| Your Whittier-area agency | Set by your city or sanitation agency for your address. | Ask for the rule and your permit conditions in writing. |
The 25 Percent Rule In Plain Terms
A grease interceptor works by letting wastewater slow down so fats float and solids sink. When the grease layer and the settled layer together fill a quarter of the liquid depth, the device has little room left to separate, and grease starts passing into the sewer line.
That is why a fixed schedule is only a starting point. A busy kitchen with fried food can reach 25 percent well before the minimum date, and the device should be serviced then. Many programs also let the agency raise your frequency if it finds grease over the limit between visits.
Records Inspectors Commonly Ask To See
Documentation proves you maintained the device even when something goes wrong.
- A cleaning log posted near the device, with dates, who cleaned it, and what was removed.
- Receipts or manifests from a licensed grease hauler for each pump-out. Some California programs ask you to keep them for three years.
- A note on the depth of the grease and solids layer at each check, so you can show it stayed under 25 percent.
- Evidence that baffles were replaced after each cleaning.
- Any correspondence with the sewer agency about your permit and cleaning frequency.
Kitchen Drain Backing Up?
Call the emergency line. A camera and a jetter can clear the line and show if grease is the cause.
A Simple Maintenance Routine
Check
Measure the layer depth on a set schedule.
Schedule
Book the hauler before the layer reaches 25 percent.
Record
Log every service and keep the hauler's receipt.
Review
If the device fills early, ask for a shorter interval.
Habits That Protect The Trap And The Drain
Scrape before washing
Dry-scraping plates keeps solids out of the sink and the device.
Skip hot water flushing
Hot water can push grease past the device, where it cools and clogs the line.
Never wash grease to a storm drain
Outdoor mop water and spills must not reach storm drains.
Clean downstream lines
A device can be fine while the line after it collects grease. Jetting keeps it open.
Standards And Sizing
Gravity grease interceptors are sized under the Uniform Plumbing Code (UPC), and agencies often require products certified by IAPMO. The California Plumbing Code is based on the UPC, so new or remodeled kitchens should plan the interceptor with that in mind. Undersized devices fill faster, which means more pumping and more risk.
If your kitchen has been remodeled, ask whether the interceptor was sized for the new fixtures. Adding sinks and a dish machine without revisiting the device is a common cause of early overflows.
Odor is an early warning. A sour smell near the device or a slow floor drain often shows up before a backup does, so treat it as a reason to check the layer depth now and not at the next scheduled service.
Catching a full device early costs one extra pump-out, while a backed-up kitchen costs a day of service and a plumber's emergency visit. Put the next service date on the calendar the day a pump-out is finished.
When Grease Reaches The Line
If grease has already coated the line, drain jetting scours the pipe wall and a camera shows how much remains. Restaurants and shops can start with commercial plumbing service for repairs and tenant improvements, and an ordinary stoppage begins with cable and camera drain cleaning.
Santa Fe Springs mixes homes and industry, and kitchens there often serve workers from nearby plants, which can mean heavy lunch-hour loads on a device sized for less.
Small Trap Or Large Interceptor
The device decides who does the cleaning and how often you need to look at it.
Small trap under a sink
- Holds a small volume, so it fills faster.
- Often cleaned by trained staff if the agency allows it.
- Needs frequent checks against the 25 percent mark.
- Easy to neglect because it is out of sight.
Large gravity interceptor
- Usually buried outside with manhole access.
- Pumped by a licensed hauler.
- Often has a minimum pump-out schedule.
- Sized under the plumbing code for the fixtures served.
Questions To Ask Your Sewer Agency
Rules differ by city and sanitation district, so get your answers in writing.
- What device is required for my kitchen, and what size?
- What is my minimum cleaning frequency, and does the 25 percent rule apply to me?
- Who can clean it, and does the agency keep a list of approved haulers?
- What records must I keep, and for how long?
- How and how often will the agency inspect, and what happens if the layer is over the limit?
Grease Trap Questions
A grease interceptor should be cleaned before floating grease and settled solids together reach 25 percent of its liquid capacity.
It depends on your agency. Some California cities set a minimum such as every 90 days or every six months. Ask your sewer agency for your requirement.
Large interceptors are typically cleaned by a licensed grease hauler. Small traps under sinks can be cleaned by staff if your agency allows it.
Some California programs ask for three years of hauler receipts. Confirm the period with your agency.
No. Hot water can carry grease past the device, where it cools and coats the line.
Ask whether the interceptor was sized for the new fixtures. An undersized device fills faster and needs more frequent service.