RCW 7.52.020

The interest of all persons in the property shall be set forth in the complaint specifically and particularly as far as known to the plaintiff, and if one or more of the parties, or the share or quantity of interest of any of the parties be unknown to the plaintiff, or be uncertain or contingent, or the ownership of the inheritance depend upon an executory devise, or the remainder be a contingent remainder, so that such parties cannot be named, that fact shall be set forth in the complaint.