RCW 91.08.140: Eminent domain—Summons.

Upon the filing of the petition aforesaid a summons returnable as summons in other civil actions, shall be issued and served upon the persons made parties defendant, together with a copy of the petition, as in other civil actions; and in case any of the defendants are unknown or reside out of the state, a summons for publication shall issue and publication be made and return and proof thereof be made in the same manner as is or shall be provided by the laws of the state for service upon nonresident or unknown defendants in other civil actions. Notice so given by publication shall be sufficient to authorize the court to hear and determine the suit as though all parties had been sued by their proper names and had been personally served.