For the payment of the principal and interest on such bonds as they respectively mature and for the creation of such sinking fund as may be necessary therefor the full faith, credit and resources of the operating school unit are irrevocably pledged and there shall be levied annually by the auditor of each county wherein such operating school unit is located, and collected by the treasurer of such county in the same manner as county taxes are levied and collected, a tax, without limit, on all taxable property in such operating school unit sufficient to pay the principal and interest of such bonds as they respectively mature and to create such sinking fund as may be necessary therefor.