The metropolitan zoological park and museum district shall collect all revenues on behalf of such subdistricts and shall deposit same in separate subdistrict funds respectively. All funds collected for a subdistrict shall be kept separate and apart from any other funds and shall be drawn upon by the proper officers of the subdistrict upon submission of properly authenticated vouchers. The district may render common services to the various subdistricts including but not limited to auditing, accounting, pension servicing and payroll. In performing such services the board is hereby authorized to employ and appoint such persons as are deemed necessary, to fix compensation and to cause the removal of employees and appointees of the board. The cost of operating the district shall be borne out of the tax funds of the subdistricts based on the ratio of each subdistrict’s tax rate to the total of the tax rates of all the subdistricts. In no event shall such operating cost ever exceed five percent of the total authorized tax revenues received by all of the subdistricts.