Wash. Rev. Code § 35.58.390
Where a metropolitan municipal corporation employs a person employed immediately prior thereto by a component city or county, or by a special district, such employee shall be deemed to remain an employee of such city, county, or special district for the purposes of any pension plan of such city, county, or special district, and shall continue to be entitled to all rights and benefits thereunder as if he or she had remained as an employee of the city, county, or special district, until the metropolitan municipal corporation has provided a pension plan and such employee has elected, in writing, to participate therein.
Until such election, the metropolitan municipal corporation shall deduct from the remuneration of such employee the amount which such employee is or may be required to pay in accordance with the provisions of the plan of such city, county, or special district and the metropolitan municipal corporation shall pay to the city, county, or special district any amounts required to be paid under the provisions of such plan by employer or employee.
RCW 35.58.390
Preservation of pension rights upon acquisition of transportation system: RCW 35.58.265.
Public employment, civil service and pensions: Title 41 RCW.