Wash. Rev. Code § 35.58.070
A metropolitan municipal corporation may be created by vote of the qualified electors residing in a metropolitan area in the manner provided in this chapter. An election to authorize the creation of a metropolitan municipal corporation may be called pursuant to resolution or petition in the following manner:
A certified copy of such resolution or certified copies of such concurring resolutions shall be transmitted to the board of commissioners of the central county.
Any resolution or petition calling for such an election shall describe the boundaries of the proposed metropolitan area, name the metropolitan function or functions which the metropolitan municipal corporation shall be authorized to perform initially and state that the formation of the metropolitan municipal corporation will be conducive to the welfare and benefit of the persons and property within the metropolitan area. After the filing of a first sufficient petition or resolution with such county auditor or board of county commissioners respectively, action by such auditor or board shall be deferred on any subsequent petition or resolution until after the election has been held pursuant to such first petition or resolution.
Upon receipt of such a petition, the auditor shall examine the same and certify to the sufficiency of the signatures thereon. For the purpose of examining the signatures on such petition, the auditor shall be permitted access to the voter registration books of each component county and each component city. No person may withdraw his or her name from a petition after it has been filed with the auditor. Within thirty days following the receipt of such petition, the auditor shall transmit the same to the board of commissioners of the central county, together with his or her certificate as to the sufficiency thereof.
RCW 35.58.070