Idaho Code § 43-609
All taxes for interest on and for the redemption of such refunding bonds shall be a lien on the taxable property of the district prior to all other liens, except the lien of general, state, county and school district taxes. Taxes levied for the payment of interest shall be payable in cash only, or by means of interest coupons detached from the refunding bonds issued under the provisions of this chapter, and maturing during the year in which such taxes are by law made payable; taxes levied for the payment of principal indebtedness shall be payable in cash only, or by means of refunding bonds issued under the provisions of this chapter, and maturing during the year in which such taxes are by law made payable. All taxes for interest shall be kept by the treasurer of the district as a special fund, to be used in payment of interest only; and all taxes for the redemption of such refunding bonds shall be kept by such district treasurer as a special fund, to be used for the redemption only of the principal of such refunding bonds.
Idaho Code § 43-609