Seattle·Grease Trap Cleaning
Seattle Cafe Grease Trap Cleaning
An indoor grease trap at a Seattle cafe, pumped out and its inlet baffle removed and cleaned. The outlet-side baffle could not be removed, and a clog was found in the connected plumbing.
Septic inspections in Seattle, by the records
Every septic inspection in King County is filed with the health department, so what follows is what inspectors actually recorded in Seattle rather than a rule of thumb.
| Measure | Figure | What it covers |
|---|---|---|
| Inspections filed in Seattle, 2015–2025 | 1,441 | Every inspection is filed with the health department |
| Inspections that found a problem | 28.5% | 5.1 points above the King County average |
| Carried out at the point of sale | 800 | Of which 30.9% found a problem |
| Partial rather than full inspections | 21.9% | Region-wide, partial inspections find a problem more often |
| Past due for an inspection | 50.4% | Of the 770 whose system type is on record |
| Past twice their interval | 29.2% | A subset of the row above |
| Properties on septic in Seattle | 1,103 | System type recorded for 770 of them (70%) |
Of the inspections filed in Seattle over the decade to 2025, 28.5% recorded a deficiency — 5.1 points above the King County average. A deficiency is an inspection filed with a status of Deficient, and the records carry no severity field, so it covers everything from a missing riser lid to a failed drain field. It is not the same thing as a broken system.
Roughly 56% of the inspections here happened because a property was changing hands, and 30.9% of those found something. Washington requires an inspection at sale whatever the system type, so that group is a complete count of a defined event rather than a sample.
How often you are due depends on what kind of system you have, so this can only be measured where the type is on record. In Seattle that is 770 of the 1,103 septic properties — 70%. Of those, 50.4% have no inspection filed within their interval and 29.2% are past twice it. The rest cannot be assessed either way, and nothing here should be read as a finding about them.
If you do not know where your own system stands, we can tell you: there is more on what an inspection covers, who is allowed to carry one out and what the records show region-wide on our septic inspections page.
What the rules require in Seattle
On-site sewage in King County is governed by Board of Health Title 13, adopted in February 2025 and in effect since 1 April 2025. Inspection frequency comes from Table 13.60-1: a gravity system without a pump is monitored every three years; public-domain technology — mounds, intermittent sand filters and pressure distribution — and proprietary treatment units are monitored every year. A newly installed system gets its first inspection six months after occupancy, or 45 days for a proprietary or commercial system.
King County is unusual in who may do the work. On a gravity system without a pump the owner may perform the routine monitoring themselves, as may a licensed maintainer or a licensed OSS pumper. Anything with a pump, and anything in a marine recovery area, requires a licensed maintainer. The report goes to you at the time of the inspection and to the health officer within thirty days.
Solids have their own separate rule: the owner must determine the level of solids and scum at least every three years for a residential system with no garbage grinder, and every year if a garbage grinder is installed.
Selling a home in Seattle triggers its own inspection. Before title transfers the seller must have a property transfer monitoring and performance inspection carried out by a licensed OSM, unless one was performed in the previous twelve months and the property has not changed hands since. The owner must also give the buyer the maintenance records if they have them.
Sources: King County Board of Health Title 13, Sections 13.60.005, 13.60.020 and 13.60.030, and Table 13.60-1. Revised OSS codes · Records search
