(1) Revenue bonds issued as provided in section 23-3617 shall not be a general obligation of the county but shall be paid only out of the revenue received from the usage fees as provided in section 23-3618.

(2) If a usage fee is charged as a part of the revenue as provided in subsection (1) of this section, a sufficient portion shall be set aside as a sinking fund for the payment of the interest on such revenue bonds and the principal at maturity.

(3) The usage fee for the service of the sewerage disposal system and plant or plants as provided in subsection (1) of this section shall be sufficient, at all times, to pay the cost of operation and maintenance of such system, to pay the principal and interest upon all revenue bonds issued pursuant to section 23-3617, and to carry out any covenants that may be provided in the resolutions authorizing the issuance of any such bonds.

(4) The holders of any of the revenue bonds or any of the coupons of any revenue bonds issued under such section, in any civil action, mandamus, or other proceeding, may enforce and compel the performance of all duties required by this section and the covenants made by the county board in the resolution providing for the issuance of such bonds, including the making and collecting of sufficient rates or charges for the specified purposes and for the proper application of the income therefrom.