Mich. Comp. Laws § 101.4: Board of public works; sewer districts; plats submitted to councils; adoption, filing.

Sec. 4.

Such plan shall, in the discretion of the board, be formed with a view to the division of the city into main sewer districts, each to include 1 or more main or principle sewers, with the necessary branches and connections; the districts to be numbered and so arranged as to be as nearly independent of each other as may be. Plats or diagrams of such plan, when completed, shall be submitted to the council, and when adopted by the council shall be filed in the office of the clerk of the board.