All bonds issued under this Act are payable solely from the revenue derived from the operation of the sewerage system. These bonds shall not, in any event, constitute an indebtedness of the sanitary district within the meaning of any constitutional or statutory limitation. It shall be plainly stated on the face of each bond that the bond has been issued under this Act and that it does not constitute an indebtedness of the sanitary district within any constitutional or statutory limitation.
70 ILCS 3010/5