Wash. Rev. Code § 35.58.400
Where a metropolitan municipal corporation employs a person employed immediately prior thereto by a component city or county or by a special district, the employee shall be deemed to remain an employee of such city, county, or special district for the purposes of any sick leave credit plan of the component city, county, or special district until the metropolitan municipal corporation has established a sick leave credit plan for its employees, whereupon the metropolitan municipal corporation shall place to the credit of the employee the sick leave credits standing to his or her credit in the plan of such city, county, or special district.
Where a metropolitan municipal corporation employs a person theretofore employed by a component city, county, or by a special district, the metropolitan municipal corporation shall, during the first year of his or her employment by the metropolitan municipal corporation, provide for such employee a vacation with pay equivalent to that which he or she would have been entitled if he or she had remained in the employment of the city, county, or special district.
RCW 35.58.400
Preservation of sick leave, vacation, and other benefits upon acquisition of transportation system: RCW 35.58.265.