Wash. Rev. Code § 4.14.010
Whenever the removal of such action to superior court is required in order to acquire jurisdiction over a third party defendant, who is or may be liable to the defendant for all or part of the judgment and resides outside the county wherein the action was commenced, any civil action which could have been brought in superior court may, if commenced in district court, be removed by the defendant or defendants to the superior court for the county where such action is pending if the district court determines that there are reasonable grounds to believe that a third party may be liable to the plaintiff and issues an order so stating.
Whenever a separate or independent claim or cause of action which would be removable if sued upon alone is joined with one or more otherwise nonremovable claims or causes of action, the entire case may be removed and the superior court may determine all issues therein, or, in its discretion, may remand all matters not otherwise within its original jurisdiction.
This section does not apply to cases originally filed in the small claims department of a district court, or transferred to the small claims department pursuant to RCW 12.40.025, except as set forth in RCW 12.40.027.
RCW 4.14.010