Wis. Stat. § 62.185: Sewer district bonds.

Whenever a city is divided into sewer districts, bonds may be issued against any such district for the purpose of paying the district’s portion of any sewer. Said bonds shall be issued in the manner authorized and provided by ch. 67. Such bonds shall not be a general city obligation but shall be payable both as to principal and interest, solely out of the special sewer district tax provided by s. 62.18 (16). Any bonds heretofore authorized to be issued in accordance with this section shall be legal, valid and binding, to the same extent as if such district, at the time of authorizing such bonds, had the power to issue the same.