Wash. Rev. Code § 53.04.150
A port district that is less than countywide, and that is located in a county with a population of less than ninety thousand and located in either the Interstate 5 or Interstate 90 corridor, may petition for annexation of an area that is contiguous to its boundaries, is not located within the boundaries of any other port district, and contains no registered voters. The petition must be in writing, addressed to and filed with the port commission, and signed by the owners of not less than seventy-five percent of the property value in the area to be annexed, according to the assessed value for general taxation. The petition must contain a legal description of the property according to government legal subdivisions or legal plats, or a sufficient metes and bounds description, and must be accompanied by a plat outlining the boundaries of the property to be annexed.
RCW 53.04.150
Intent-1999 c 250 ss 2-5: "The legislature intends annexation procedures set forth in sections 2 through 5 of this act to be alternative methods available to port districts that are less than countywide. The legislature does not intend the alternative procedures to supersede any other method authorized by chapter 53.04 RCW or other law for annexation of territory to a port district." [ 1999 c 250 s 1.]