The representative of each subdistrict advisory board chosen pursuant to section 204.571, together with the mayor or chief executive officer or the authorized representative of every incorporated municipality and a representative authorized in writing to act in that capacity of every subdistrict, which lies partially within the district and which operates a sewage collection system which will discharge sewage into the trunk sewers or the sewage facilities of the common sewer district shall constitute an advisory board of the district. If there are three or fewer municipalities and subdistricts the organization of an advisory board is optional at the discretion of the board of trustees, and in such case all powers can be exercised by the board of trustees without the concurrence of the advisory board. The advisory board shall organize by electing one of its members as chairman and one as vice chairman. The board of trustees shall keep the advisory board informed as to all phases of the planning and operations of the district, and the advisory board shall make such recommendations to the board of trustees as it deems advisable with regard to the construction and operation of the sewers and facilities of the district.