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.