The rents and receipts of said corporation for the use of sewerage shall first be applied to pay the annual principal and interest as it becomes due upon sewerage bonds issued by said corporation, and whenever such rents and receipts shall exceed the amount required to pay such principal and interest, and the interest of any other sewerage bonds of said corporation to pay such excess, in the necessary repairs, management, and addition to said sewerage; and the balance of such excess, if any, shall be applied to Sewerage Department operations for ensuing years. Any deficit shall also be applied to Sewerage Department operations for ensuing years.