The American Civil Liberties Union of Washington has published an online resource on how to obtain a court order waiving or reducing the interest that accrues on legal financial obligations.  The packet contains information regarding the Washington state laws that govern the process, as well as step-by-step instructions and court forms for completing the  procedure yourself.  For more information, please use the following links:

Interest Waiver Guide (from the ACLU)

Revised Code of Washington (RCW) Title 10.82.090 – Interest on Judgments