Grease Trap Cleaning: How Often Restaurants Really Need It

What does a grease trap actually do?

Everything that leaves a kitchen sink leaves warm. Fats and oils stay suspended in the water while it is hot, then they cool, separate out, and stick to whatever they touch. A grease trap is a box that slows the flow long enough for that separation to happen inside the box instead of out in your lateral. Grease floats up, food solids settle out, and the clearer water in the middle leaves through a baffle.

That is the whole mechanism, and it explains why a full trap stops helping you. As the grease layer thickens from the top and the solids pile up from the bottom, the quiet middle disappears. Water pushes straight through at speed and carries the grease out with it. An unpumped trap is not working at half capacity. It is a length of pipe with a lid on it.

The federal rule underneath all the local ones is one sentence. The National Pretreatment Program, at 40 CFR 403.5(b)(3), bars "solid or viscous pollutants in amounts which will cause obstruction" from a public sewer. EPA's fact sheet for food service establishments spells out why agencies care. Its Report to Congress on sewer overflows found grease from restaurants, homes and industrial sources to be the most common cause of reported blockages, at 47 percent. The same sheet puts one restaurant's annual grease output at 800 to 17,000 pounds. EPA's fact sheet is here.

How often does grease trap cleaning need to happen?

There is no national interval, and that is where most owners go wrong. Your sewer agency sets it, usually in your food service discharge permit, and the number moves from city to city. Outdoor gravity interceptors tend to run on a 90 day cycle. Small indoor traps run far shorter, down to weekly in some jurisdictions. San Jose's guidance tells food service establishments to pump when the final chamber is twenty five percent full of grease and solid food waste, or within 90 days of the last pumping, whichever comes first. Pleasanton tells users to inspect at least monthly and will not accept more than 60 days between maintenance.

EPA says plainly that the correct interval is a fact about your kitchen rather than your equipment. The required frequency "depends greatly on the amount of FOG a facility generates" along with whatever you do upstream to keep grease out of the drain in the first place. Two kitchens with identical 1,000 gallon interceptors can sit on different schedules. A sandwich shop and a place running three fryers are not the same account, and the agency will say so once it has read a few of your pump reports.

So get the permit out and find your number, then check the trap between pump-outs, because that interval is a ceiling, not a promise.

How do I tell when the trap is full?

Measure it. A dipstick and a log settle in two minutes what guessing never will.

Santa Rosa's Department of Utilities states its limits in inches rather than percentages, which is handy, because you can check inches without a hauler on site. Its FOG enforcement policy makes it a violation to allow a grease trap rated 100 lbs or smaller to hold 3 inches or more of grease and solids. On a larger grease interceptor the limits are 12 inches on the inlet side or 6 inches on the outlet side. The city's policy document lays out the full schedule.

Watch the outlet number hardest. Six inches on the outlet side means grease has already cleared the baffle and is sitting at the point where water leaves for the city main. Buildup on the inlet side is the trap doing its job. Buildup on the outlet side is next month's blockage, already paid for.

What does it cost to skip it?

Two bills, and they can arrive in either order.

One is the blockage. Grease that has cooled in a lateral sets up dense and waxy. A cable tends to bore a hole through it and leave the walls coated, so the line closes again within weeks. Clearing it properly means jetting. On our own drain work, a jetting job on a line packed with heavy grease or roots runs $600 to $1,400, where a routine residential jetting sits at $400 to $700. A restaurant lateral lands at the top of that range, and it fails during service rather than at ten on a Tuesday morning.

The other bill is the agency. Santa Rosa's fine schedule steps up with each repeat: a warning first, then $100 on the second grease removal device violation, $250 on the third, $500 on the fourth, and $1,000 with a cease and desist order on the fifth. For interceptors the fourth step is $1,500. The bottom row of the table is termination of service, which for a restaurant means closed. This is not a Sonoma County quirk. EPA notes that New York City went to a $1,000 per day fine for FOG violations after finding a 73 percent non-compliance rate with its grease trap ordinance.

The paperwork is part of the job

Santa Rosa requires three years of records kept on site: hauler receipts if someone pumps it for you, or a current cleaning log if your own crew handles it. An inspector reads a pumped trap with no paperwork the same way as an unpumped one. Put the receipts in the same binder every time, and write your measured depths in it too.

Who handles which part of this?

Pumping the trap and hauling the waste off site is a licensed grease hauler's work, regulated separately from your building. The plumbing is a different job: the baffles, the standpipe, the inlet and outlet piping, and the line out to the main. Santa Rosa lists "failure to maintain grease removal device in proper working condition" as its own violation and names broken baffles and standpipes specifically, so a cracked baffle earns a citation even with a current pump receipt in the binder.

That second half is ours. CNTRline does commercial plumbing for restaurants and property managers across Sonoma and Marin County, including the drain and sewer lines downstream of a trap, and we schedule work outside service hours so a kitchen does not lose a lunch rush to it. If the line leaving your trap is already draining slow, get it looked at before it closes. Call (707) 308-5599.