The Washington State Department of Labor & Industries has general information and a more detailed publication about filing a lawsuit against a contractor's bond.
Washington LawHelp also has some information about filing this type of lawsuit.
Self-help kit from the law library
The law library sells a Start a Contractor's Bond Claim self-help kit with forms and instructions to start a claim against the contractor's bond (it does not cover how to finalize the process). It includes forms for either the homeowner or a subcontractor/supplier who has not been paid to use. Kits can be purchased at the library or online and mailed out.