At the time specified in § 10-12-26 in every township where there are bonds outstanding, the township board of supervisors shall levy a tax sufficient to pay the interest on such bonds and not to exceed fifteen percent of the principal of such debt, as a debt service fund, the money from which tax shall be applied to no other purpose than the payment of outstanding bonds and interest on the same, until such bonds and interest are fully paid, when any surplus remaining shall be transferred to the township general fund, the amounts of which levy shall be certified as prescribed in § 10-12-26.
SDCL 10-12-27