The process of filing a Washington lien release is very similar to filing the actual mechanics lien claim itself. It is a simple document that references the mechanics lien recording information such as the filing date, document number, page number, etc. This should be filed in the county recorder's office where the original lien was filed. You can download a free, customizable template of a WA mechanics lien release form here.
For a little more information see: How to Cancel a Washington Lien