Immediately after their organization, the directors shall enter an order directing the issuance of bonds for such district within the limits authorized by the election held therefor, sufficient to cover the cost of the proposed improvements, all of the expenses incident thereto, and the expenses necessarily incurred in connection with the creation and establishment of the district; and they shall levy a tax upon all property subject to taxation in the district, sufficient to pay the interest on such bonds, with an amount to be placed in the sinking fund sufficient to redeem said bonds at maturity, and such levy shall remain as a levy for such purpose until a new levy is made.