At a glance
| Who regulates | Your local health jurisdiction, under WAC 246-272A (WA Department of Health) |
|---|---|
| Inspection when a home is sold | Required from Feb 1, 2027. From February 1, 2027: an inspection by a third-party inspector authorized by the local health officer at every property transfer. Sellers must also hand over all available maintenance and repair records. |
Septic tank size in Washington
From WAC 246-272A-0232:
| Home | Minimum tank |
|---|---|
| Up to 4 bedrooms | 1,000 gal |
| Each extra bedroom | +250 gal |
Compare with other states on our tank size calculator.
Routine inspections
- At least once every three years for a system that is only a septic tank and gravity drain field.
- Every year for all other systems, unless the local health officer requires more often.
At sale (from February 1, 2027)
- Inspection by a third-party inspector authorized by the local health officer.
- Proprietary treatment products inspected per the manufacturer's recommendations.
- Results submitted to the local health jurisdiction on its approved form.
- The local health officer may waive it if a recent compliant inspection is on file.
What you can't put in the system
- Additives not specifically approved by the Department of Health.
- Strong acids, bases or chlorinated solvents for cleaning the system.
Costs
We don't yet have checked Washington-specific prices. National figures: pumping averages about $420–$430 (pumping cost), inspections about $550 on average (inspection cost), and a conventional system $3,000–$8,500 installed (installation cost).
Rules change, and counties and towns can be stricter than the state. Confirm with the agency above before you buy, sell or build.