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Sales and transfers of properties with on-site sewage/septic systems

Learn about the special requirements for the sale and transfer of properties with septic systems.

Statewide OSS rule revision process

The Washington State Board of Health is revising the statewide OSS rules. You can learn more about this process, including how to comment, on the state Department of Health’s website: On-site Sewage System Rule Revision.

Buying or selling a property with an on-site sewage/septic system

King County properties with a septic system must have their system inspected by a certified on-site system maintainer before the transfer of title.

Schedule an inspection

Sellers will need to schedule the inspection with a certified on-site system maintainer.

Find an on-site system maintainer in King County

Waiving the inspection

An inspection can be waived if one of the following apply:

  • An Operation/Performance Monitoring Report has been performed by a licensed on-site system maintainer within the last 6 months. Reports for this on-site sewage system have been filed with Public Health - Seattle & King County on a regular basis.
  • The property is new construction, and the home has never been occupied. This requires proof of vacancy.
  • A permitted on-site sewage system is installed, and the first inspection is not yet due. You have 45 days use for proprietary systems, and 6 months use for gravity and public domain technology systems.
  • The on-site sewage system has been abandoned due to residence connecting to public sewer, or land converting to public use.

Download a waiver form for property transfer inspection (49 KB)

Property transfer inspection reports

  • After your certified on-site system maintainer performs the inspection, they will submit a report to Public Health - Seattle & King County.

View a sample report (19 KB)

  • Public Health staff will review the report within 10 business days.
  • You can view On-site Sewage System Property Transfer Inspection Reports at
    • Search for the property of interest, then look in the "Application History".

Seller Notice of On-site System Maintenance Requirements

Before closing sellers must record a Notice of On-site Sewage System Operation and Maintenance Requirements (OSSM) at the King County Recorder's Office. This is also known as the Northwest Multiple Listing Service form #22U. 

If the Notice is already recorded on title, this requirement is complete. The seller does not need to record the Notice again. The seller must give a copy of the recorded OSSM to the buyer before closing.

Buyer responsibilities

At the time of property transfer, the buyer must submit the required Operation and Maintenance Program fee to Public Health. Visit Public Health’s portal to pay online. The buyer will receive information regarding good practices for maintaining septic systems.