If it appears that the required percentage of the voters of the subdistrict voting on the proposition of incurring indebtedness submitted at an election pursuant to subsections 3 to 7 of section 204.250 were in favor of incurring such indebtedness, the election authority shall make an order reciting the holding of such election and the results thereof, both for and against the proposition, and if the result of the election as certified shall be in favor of incurring the indebtedness and issuing the bonds, or if the required percentage of the voters of the common sewer district have, prior to the creation of the subdistrict, voted in favor of incurring indebtedness and the amount of bonds issued under such authority does not exceed the amount approved by the voters at such election, then the board of trustees for the common sewer district may direct the issuance of such bonds to the amount of the debt authorized to be incurred, or any portion thereof, and shall either before or at the time of doing so provide for the collection of an annual ad valorem tax upon all of the taxable property within the subdistrict, which tax shall be sufficient to pay the interest on such indebtedness as it falls due, and also create a sinking fund for the payment of the principal thereof within twenty years from the date of contracting the same, such tax to be levied and collected as provided for in section 249.130.