Wash. Rev. Code § 7.70A.020
(1) Parties in an action covered under RCW 7.70A.010 may elect to submit the dispute to arbitration under this chapter in accordance with the requirements in this section.
(2) A party that does not initially elect to submit a dispute to arbitration under this chapter must file a declaration with the court that meets the following requirements:
[ 2006 c 8 s 306.]