Why Sewer Districts Require a Grease Trap Log
A grease trap (also called a grease interceptor) exists to catch fats, oils, and grease — FOG — before they reach the public sewer line. Left unchecked, FOG cools and hardens inside pipes, and enough of it building up in a shared municipal line causes a sanitary sewer overflow: raw sewage backing up into streets, basements, or waterways. Because a single food-service kitchen can contribute a disproportionate share of the FOG entering a district's system, most sewer authorities run a dedicated FOG program that requires regular pumping and, critically, proof it happened. A cleaning log is that proof. It's the difference between "the trap probably gets serviced" and a dated, itemized record a district inspector can check against their own pump-out schedule.
The stakes are higher than a typical health-code paperwork item. Sewer districts that find an unmaintained trap — or no log at all — routinely issue fines that scale with the size of the overflow risk, and repeat violations can lead to a suspended discharge permit, which in practice means the kitchen can't legally operate until it's resolved. A five-minute log entry after every pump-out is cheap insurance against a bill, and a business interruption, that isn't.
How Often Should You Pump Your Grease Trap?
The industry standard is the 25% rule: once the combined layer of grease, oil, and floating solids reaches a quarter of the trap's total liquid depth, it's time to pump it out. Waiting longer lets FOG start passing through into the line instead of separating out, which defeats the point of having a trap at all. In practice that 25% mark arrives faster than most operators expect — a busy single-truck operation running a fryer daily often hits it monthly, while a lower-volume truck or a commissary with lighter grease output might stretch to a quarterly interval. Some sewer districts skip the 25% rule entirely and simply mandate a fixed interval (commonly every 60 or 90 days) regardless of measured depth, so check your permit or discharge agreement for a specific number before assuming your own usage pattern sets the schedule.
Undersized traps on high-volume trucks are a common trap (no pun intended) — a unit rated for a much smaller kitchen fills past 25% within a couple of weeks of heavy fryer use. If your log shows the trap consistently needs pumping far more often than the interval your district expects, that's usually a sign the interceptor itself is undersized for your equipment, not that your crew is doing something wrong.
What an Inspector Checks For
A sewer-district or health inspector reviewing your grease trap program typically wants three things lined up: a complete, dated log with no unexplained gaps longer than your required interval; a hauler that's actually licensed to transport and dispose of grease waste in your jurisdiction (an inspector may cross-check your manifest numbers against the hauler's own registration); and physical evidence the trap itself has been kept in working condition — no visible overflow staining, a lid that seals, and baffles that haven't been bypassed or removed. A log with real gallons/inches figures and a manifest number for every row is what turns "we clean it when it needs it" into a record that survives that cross-check.
Keep both a physical and a digital copy if you can. A paper log lives on the truck or in the commissary where it gets filled in, but a phone photo taken after each pump-out protects the record if a sheet gets lost, soaked, or left behind in a vehicle that's out of service. File the digital copies with your other compliance paperwork — permit, commissary agreement, and hauler manifests — so a single folder answers whatever a district inspector asks for in one sitting. Most jurisdictions expect at least 1–2 years of completed logs on file; check your local discharge permit for the exact retention period, and follow the stricter of the two if state and local rules differ.
How Much Does Grease Trap Pumping Cost?
Pricing scales with trap size and how much grease and solids actually come out, not a flat per-visit number. Small indoor interceptors (20–50 gallons) typically run $150–$400 per service; mid-size floor-mount units land around $200–$450 routine; large outdoor interceptors (500–2,500 gallons) run $300–$1,500 per service; and industrial-scale units can exceed $800. Most haulers charge a base service fee plus a per-gallon rate for what's actually pumped, so a trap that's overdue and full costs more to service than the same trap pumped on schedule (GreaseTrapLocator, 2026 pricing guide; PumpLocal).
A single-truck or small-commissary operation on a monthly-to-quarterly schedule typically lands in the $1,200–$3,600 a year range for pump-out service alone, before any hydro-jetting or emergency call-outs (GreaseTrapLocator). Two things push the price well above the low end of these ranges: letting the trap run past the 25% mark, which several haulers price at a premium since it takes longer to service and haul away, and calling for emergency or after-hours service, which commonly adds 50–100% over a scheduled visit. Booking routine pump-outs on a fixed schedule — the whole point of the log above — is what keeps you on the cheaper end of these numbers.
Whoever pumps your trap will also want to see this log, or at minimum your last service date, before they quote a price — a trap that's clearly overdue gets priced (and serviced) differently than one on a normal cycle. Keep it up to date and hand it over when you call for a quote, not just when an inspector asks.
Sizing: Why the Same Trap Doesn't Work for Every Truck
Grease traps and interceptors are sized by flow rate and grease retention capacity, not by vehicle size, so two trucks with identical footprints can need very different units depending on what's cooked. A truck running a single flat-top and a dish sink produces far less FOG than one running a deep fryer plus a griddle at full volume on a Saturday night. If your log shows the 25% mark arriving in days rather than weeks, that's a sizing problem, not a scheduling one — pumping more often is a workaround, not a fix, and most sewer districts would rather see a right-sized interceptor than a log full of emergency pump-outs. A plumber familiar with your local plumbing code can confirm whether your current unit matches your actual grease load.
Common Mistakes That Trigger a FOG Violation
The most common issue inspectors flag isn't a missed pump-out — it's a log with gaps that don't match the trap's visible condition. A trap that's clearly overdue (grease visible near the lid, odor, slow drains) next to a log claiming it was serviced on schedule reads as falsified records, which districts treat far more seriously than a late pump-out on its own. Other frequent triggers: pouring used fryer oil or bulk grease down a drain instead of into a separate collection container (this bypasses the trap's rated capacity entirely and is banned outright in most FOG ordinances); using an unlicensed or informal hauler who can't produce a manifest; and removing or propping open interior baffles to "improve drainage," which defeats the separation the trap exists to do and is usually visible to an inspector on sight.
None of these are hard to avoid once the log itself becomes a habit. Treat every pump-out the same way you'd treat a required food-safety check: it happens on the interval your permit sets, a real person signs their name to it, and the paperwork goes in the folder the same day — not reconstructed from memory the week before a scheduled inspection.