Any municipality may enter into contracts or agreements with any persons for: (1) The repair, maintenance and operation and management of the facilities and properties of the combined system, or any part thereof; or (2) the collection and disbursement of the income and revenues thereof, or for both (1) and (2), for the period of time and under terms and conditions as shall be agreed upon between the municipality and such persons. Any municipality shall have plenary power and authority to provide in the ordinance authorizing the issuance of bonds hereunder, or in any trust indenture securing the bonds, that the contracts or agreements shall be valid and binding upon the municipality as long as any of the bonds, or interest thereon, is outstanding and unpaid.