Nothing in this Act shall impair the security of any indebtedness of the former district incurred before the effective date of this Act. The new district shall be obligated for such indebtedness, and the direct annual tax provided for in accordance with Section 16 of “An Act to create sanitary districts in certain localities, to drain and protect the same from overflow for sanitary purposes and to provide for sewage disposal”, approved May 17, 1907, as amended, to pay the interest on and principal of such indebtedness shall continue to be levied and extended until such indebtedness has been paid in full.