The following are links to information by county for looking up property parcel/tax numbers, asbuilts, online reports (RME). and the Washington On-Site Sewage Association (WOSSA). You can use these links to research specific property information and general information related to on-site systems for the listed counties.

See below for the links for county web sites and for Septic as-builts.
You can also map the areas for all of these counties in the parcel/tax numbers websites.