If a city, village or incorporated town exercises the powers granted by this Division 19 jointly and cooperatively with another city, village or incorporated town or county and it is agreed pursuant to the provisions of Section 11-19-7 that there shall be a joint garbage department to be operated as an intermunicipal function, employees assigned to such department shall nevertheless be considered employees of the appropriate individual city, village or incorporated town. The administrative head or superintendent of any such joint department shall be an employee of and shall be appointed by the mayor or president of the largest city, village or incorporated town participating in the joint department, but such appointment shall be subject to confirmation by the joint committee on operations provided for in Section 11-19-7. Any rights, privileges or benefits, civil service status, pensions or otherwise, existing or hereinafter created, appertaining to any municipal employee assigned to any joint garbage department shall continue to exist as rights, privileges or benefits without regard to such assignment and as if this amendatory act of 1957 had not been adopted.