The county treasurer of each county in which there is a city of the first class is ex officio collector of city taxes of such city, and before entering upon the duties of office the treasurer shall execute in favor of the city and file with the clerk thereof a good and sufficient bond, the penal sum to be fixed by the city council, such bond to be approved by the mayor of such city or other authority thereof by whom the bond of the city treasurer is required to be approved. All special assessments and special taxation for local improvements assessed on property benefited shall be collected by the city treasurer.
RCW 36.29.100