Wash. Rev. Code § 53.12.115
A ballot proposition shall be submitted to the voters of any port district authorizing an increase in the number of port commissioners to five whenever the port commission adopts a resolution proposing the increase in number of port commissioners or a petition proposing such an increase has been submitted to the county auditor of the county in which the port district is located that has been signed by voters of the port district at least equal in number to ten percent of the number of voters in the port district who voted at the last general election. The ballot proposition shall be submitted at the next general or special election occurring sixty or more days after the petition was submitted or resolution was adopted.
At the next general or special election following the election in which an increase in the number of port commissioners was authorized, candidates for the two additional port commissioner positions shall be elected as provided in RCW 53.12.130, and the voters may be asked to approve the nomination of commissioners from district-wide commissioner districts as permitted in RCW 53.12.010(2).
RCW 53.12.115