RCW 35.50.250: Procedure—Summons and service.

In foreclosing local improvement assessments, if the lot, tract, or parcel contains a residential structure with an assessed value of at least two thousand dollars, the summons shall be served upon the defendants in the manner required by RCW 4.28.080. For all other lots, tracts, or parcels the summons shall be served by either personal service on the defendants or by certified and regular mail.