Wash. Rev. Code § 26.27.441
(1) A child custody determination issued by a court of another state may be registered in this state, with or without a simultaneous request for enforcement, by sending to the appropriate court in this state:
(2) On receipt of the documents required by subsection (1) of this section, the registering court shall:
(3) The notice required by subsection (2)(b) of this section must state that:
(4) A person seeking to contest the validity of a registered determination must request a hearing within twenty days after service of the notice. At that hearing, the court shall confirm the registered determination unless the person contesting registration establishes that:
[ 2001 c 65 s 305.]