For the purpose of meeting the indebtedness evidenced by the said funding bonds the county board shall cause to be annually levied upon all the real and personal property within the precinct or within the limits of the former or de facto precinct against which the said bonds have been adjudged to be a liability, a tax sufficient to pay the annual interest upon the said funding bonds, and not less than five percent of the principal, for the purpose of creating a sinking fund to pay the principal at maturity, and at the tax levy preceding the maturity of such bonds shall levy an amount sufficient to pay the principal and the remaining interest due on said bonds.