In all first class counties in which a charter form of government is adopted, the county commission, upon written request from all districts in the county, within sixty days prior to the effective date of the new charter form of government, shall by resolution, order, or ordinance, appoint five trustees, the majority of whom shall reside within the boundaries of the district. In the event there is more than one district within the county organized pursuant to this chapter the majority of the trustees appointed shall reside within the district having the greatest number of customers. The trustees, whose term shall begin on the same date that the charter form of government becomes effective, shall be responsible for the control and operation of all such sewer districts organized pursuant to this chapter in the county, and shall have the same powers and duties as the county commission as provided in this chapter. The term of each trustee shall be five years, except that, of the first board appointed, one member shall serve for one year, one member shall serve for two years, one member shall serve for three years, one member shall serve for four years, and one member shall serve for five years. All vacancies after the initial appointment shall be filled by the county executive officer with the concurrence of the governing body of the county as constituted under the charter form of government. The trustees shall be reimbursed by the district for all reasonable expenses incurred in the performance of their duties, which amount shall not exceed the sum of twenty-five dollars per month.