If the public works herein provided be constructed and operated by the municipalities acting jointly, the local authorities of the contracting municipalities or districts having charge of sewage shall jointly supervise the construction and operation of such sewage system, or they may jointly engage or employ a competent sanitary engineer for such purpose. They shall jointly elect or appoint all necessary employees at the disposal plant and for the care of the trunk line sewer, and severally appoint such employees as they may be authorized so to do by the respective governing bodies to work on the system within the bounds of such municipality.
New York Legal Code