Every city issuing bonds under the provisions of sections 95.370 to 95.400, inclusive, shall, before or at the time of doing so, provide for the levy and collection of an annual tax sufficient to pay the interest on such indebtedness as it falls due, and also to constitute a sinking fund for the payment of the principal thereof, within twenty years from the date of issue of the said bonds.
§ 95.380, RSMo