Septic inspection and pumping cost in King County (2026):
how often, what it costs and the rules when you sell
HOW MUCH DOES A SEPTIC INSPECTION COST IN THE SEATTLE AREA?
Angi puts the average septic inspection in Seattle at $611, with most between $222 and $1,000. Public Health – Seattle & King County says a conventional gravity system must be inspected every 3 years, and other systems (pressure, mound, sand filter, aerobic) every 6 months, by a King County certified pumper or on-site system maintainer. Pumping is a separate cost, done only when the inspection shows it's needed.
How often King County requires an inspection
| System type | King County | Washington minimum |
|---|---|---|
| Conventional gravity (tank + gravity drainfield) | Every 3 years | At least every 3 years |
| Pressure distribution, mound, sand filter, aerobic treatment unit, subsurface drip | Every 6 months | At least once a year |
- Who inspects: a King County certified pumper or on-site system maintainer (OSM). The maintainer sends a report on your system to Public Health.
- What they check: the septic and pump tanks, any treatment unit, the distribution system, and the drainfield and reserve areas.
- Pump only when needed. King County recommends inspecting and pumping "only when needed," and notes an inspection costs less than pumping.
Septic inspection cost
| Seattle (Angi) | Reported cost |
|---|---|
| Typical range | $222–$1,000 |
| Average | $611 |
| Low end / high end | $111 / $1,444 |
| Annual inspection | $220–$275 |
| Basic inspection | $275–$440 |
| Detailed inspection | $440–$770 |
| Camera inspection | $275–$990 |
Septic pumping cost
| Tank size | Pumping cost |
|---|---|
| 750 gallons | $175–$300 |
| 1,000 gallons | $225–$400 |
| 1,250 gallons | $275–$500 |
| 1,500 gallons | $345–$600 |
| 1,750 gallons | $400–$700 |
- Hard-to-reach tanks: buried access points or landscaping in the way add $50 to $200.
- Neglected tanks: thick sludge can add $100 to $300.
- After hours: weekend or emergency service typically runs 50% to 100% above standard rates.
- How often: This Old House says most 1,000-gallon tanks serving a family of four need pumping every 3 to 5 years. In King County, the inspection tells you when.
Selling a home with a septic system
- Inspection before title transfer. King County requires an inspection by a certified on-site system maintainer before the title transfers. Public Health reviews the report within 10 business days.
- Record the notice. Before closing, the seller records the Notice of On-site Sewage System Operation and Maintenance Requirements (NWMLS form 22U) with the King County Recorder's Office, unless it's already on title, and gives the buyer a copy.
- Buyer's fee. At transfer, the buyer pays King County's Operation and Maintenance Program fee through the Public Health Permit Center.
- Waivers. The inspection can be waived, for example, if a maintainer filed a monitoring report in the last 6 months and reports were filed regularly.
- Statewide from February 1, 2027. Washington's updated septic rule requires sellers to get a property transfer inspection by a third-party inspector authorized by the local health officer, and to give the buyer all available maintenance and repair records.
Homes on city sewer have a different check: see sewer scope inspection cost.
Frequently asked questions
How much does a septic inspection cost in King County?
Angi puts the average septic inspection in Seattle at $611, with most between $222 and $1,000. A routine annual inspection is $220 to $275, and a detailed one $440 to $770.
How often does a septic system need to be inspected in King County?
Every 3 years for a conventional gravity system and every 6 months for pressure distribution, mound, sand filter, aerobic and drip systems, according to Public Health – Seattle & King County.
How much does it cost to pump a septic tank?
This Old House, citing Angi, lists $225 to $400 for a 1,000-gallon tank and $345 to $600 for a 1,500-gallon tank. Hard-to-reach lids and neglected tanks cost more.
Do I need a septic inspection to sell my house in King County?
Yes. King County requires an inspection by a certified on-site system maintainer before the title transfers, unless a waiver applies, and the seller must record the operation and maintenance notice before closing.
Who can inspect my septic system in King County?
A King County certified pumper or on-site system maintainer. The maintainer sends a report on the system's condition to Public Health – Seattle & King County.
About these prices. The ranges are published estimates from the sources below, as of the dates shown. Material costs, labor rates, tariffs and inflation can change prices after those dates, and your home may differ. Use them to plan a budget, then get written quotes from licensed contractors.
Sources
- Public Health – Seattle & King County — Septic system inspections
- Public Health – Seattle & King County — Sales and property transfers
- WAC 246-272A-0270 — Owner responsibilities and Washington Department of Health — On-site sewage system rule revision
- Angi — Septic inspection cost in Seattle, WA
- This Old House — Cost to pump a septic tank (updated May 22, 2026)
All sources accessed November 9, 2026.
This guide summarizes published cost estimates and public health rules. Confirm your system's inspection schedule with Public Health – Seattle & King County (206-477-8050). See our disclosure and disclaimer.