Home-sale septic inspections in King County, Washington
King County: The seller must hire an inspector to check the system before the sale closes. King County Board of Health Code § 13.60.030, Operation and Maintenance at Time of Sale · checked 2026-09-23
Does King County require a septic inspection before a sale?
The seller must hire an inspector to check the system before the sale closes.
Applies to a sale or other transfer of property served by an on-site sewage system.
King County Board of Health Code § 13.60.030, Operation and Maintenance at Time of Sale · checked 2026-09-23
Who may inspect a septic system in King County?
A licensed designer inspects a new system before it is covered. Public Health then approves or denies the finished work.
King County Board of Health Code § 13.56.030, On-Site System Inspection · checked 2026-09-23
How often does King County require a septic inspection?
An inspection is due every 3 years.
Applies to a gravity system with no pump.
Other system types need a check every year. Washington's own rule sets this same interval statewide.
King County Board of Health Code § 13.60.010, Table 13.60-1 · checked 2026-09-23
Sources
Each figure on this page has a government source and a checked-on date.
- Public Health – Seattle & King County — On-site sewage/septic system program
- Public Health – Seattle & King County — About Environmental Health Services
- King County Board of Health Code §§ 13.20.030, 13.20.035, 13.68
- Public Health – Seattle & King County — OSS Permitting, Certifications, and Drinking Water Fees, effective January 1, 2026
- Public Health – Seattle & King County — Search on-site sewage/septic system records
- Washington Administrative Code § 246-272A-0232
- Washington Administrative Code § 246-272A-0210
- USDA NRCS Soil Data Access (SSURGO)
- King County — Septic System Maintenance and Side Sewer Repair Rebate Program
Verify before you act. Septic rules are set locally and they change. Check anything here before you spend money on it. Call the Public Health – Seattle & King County, On-Site Sewage/Septic System Program, on 206-477-8050.