RCW 26.18.040: Support or maintenance proceedings.

(1) A proceeding to enforce a duty of support or maintenance is commenced: (a) By filing a petition for an original action; or (b) By motion in an existing action or under an existing cause number. (2) Venue for the action is in the superior court of the county where the dependent child resides or is present, where the obligor or obligee resides, or where the prior support or maintenance order was entered. The petition or motion may be filed by the obligee, the state, or any agency providing care or support to the dependent child. A filing fee shall not be assessed in cases brought on behalf of the state of Washington. (3) The court retains continuing jurisdiction under this chapter until all duties of either support or maintenance, or both, of the obligor, including arrearages, have been satisfied.