For the payment of the bonds, both principal and interest, as they may mature, there shall be pledged the full faith, credit and taxing power of the county issuing the same, and, until the principal and interest of any bonds issued under this chapter shall be fully paid, if the levy provided for by § 57-21-140 shall be insufficient for the purpose, there shall be levied annually by the county auditor on all taxable property in the paving district and collected by the county treasurer thereof an additional sum sufficient to provide the amount necessary to pay such interest as it becomes due and to provide a sinking fund to pay such principal at the date or dates of maturity thereof, after the application to such purpose by the county treasurer of any moneys in said special fund. Such annual tax shall be levied and collected by the same officers and in the same manner as is now provided by law for the levy and collection of taxes for county purposes in the county. The money so collected shall be applied by and under the direction of the county treasurer to the payment of the principal and interest aforesaid, as they respectively become due, and pending such application such money shall be deposited or invested by or under the direction of the county treasurer.