There shall be a board of sewer commissioners consisting of five (5) members elected for terms of three years each, so arranged that the term of office of as nearly an equal number of members as is possible shall expire each year. The board of sewer commissioners shall have general charge of the care and management of the municipal sewer system, and of all property of the town relating thereto. The board of sewer commissioners shall have all of the powers and duties which are given to boards of sewer commissioners under the constitution and laws of the Commonwealth of Massachusetts, and such additional powers and duties as may be authorized by the charter, by by-law or by other vote of the town meeting.