The governing body of such city shall provide for the payment of said bonds and the interest thereon as the same becomes due and payable by the levy of a general tax on all taxable property in such city. And the governing body of any such city is hereby authorized to levy an annual tax on all taxable, tangible property in such city to be used for the purpose of maintaining and operating sewage-disposal works and to pay a portion of the principal and interest on bonds issued by such city under the authority of Kan. Stat. Ann. § 12-1774, and amendments thereto. The revenue derived from such tax, except for an amount to pay a portion of the principal and interest on bonds issued by such city under the authority of Kan. Stat. Ann. § 12-1774, and amendments thereto, shall be kept in a separate fund by the city treasurer and shall be used for no other purpose.