For the purpose of paying the cost of the improvements authorized pursuant to section 17-913, the city council of any city of the second class or village board of trustees of any village, after such improvements have been completed and accepted, shall have the power to issue negotiable bonds of such city or village, to be called Sewer Bonds, payable in not exceeding twenty years and bearing interest payable annually or semiannually, which may either be sold by the city or village or delivered to the contractor in payment for the work, but in either case for not less than their par value. For the purpose of making partial payments as the work progresses, warrants may be issued by the mayor and city council or by the village board of trustees upon certificates of the engineer in charge showing the amount of work completed and materials necessarily purchased and delivered for the orderly and proper continuation of the project, in a sum not exceeding ninety-five percent of the cost of such project and upon the completion and acceptance of the work issue a final warrant for a balance of the amount due the contractor, which warrants shall be redeemed and paid upon the sale of the bonds issued and sold. The city or village shall pay to the contractor interest at the rate of eight percent per annum on the amounts due on partial and final payments beginning forty-five days after the certification of the amounts due by the engineer in charge and approval by the governing body and running until the date that the warrant is tendered to the contractor. All special assessments which may be levied upon property specially benefited by such work or improvements shall, when collected, be set aside and constitute a sinking fund for the payment of the interest and principal of such bonds. There shall be levied annually upon all the taxable property in such city or village a tax, which, together with such sinking fund derived from special assessments, shall be sufficient to meet payments of interest and principal as the same become due. Such tax shall be known as the sewer tax and shall be payable annually in money.