Sanitary sewer districts may be created by or under authority of laws referring to sections 115.61 to 115.67 and enumerating the cities or towns, or portions thereof, which are or may be included therein. The purpose of sections 115.61 to 115.67 is to provide a method by which municipalities in a drainage area designated by law may join together to prevent water pollution in excess of reasonable standards in that area. Each district created as contemplated herein shall be responsible for planning collection, treatment, and disposal facilities for all municipalities in its drainage area, whether or not initially included within its boundaries. Any municipality, by resolution adopted by a majority of all members of its governing body, may request the annexation of all or part of its territory to the district, and the annexation shall become effective when approved by resolution adopted by a majority of all members of the board of directors of the district with the approval of the Minnesota Pollution Control Agency, or by order of the Minnesota Pollution Control Agency made under authority of Laws 1963, chapter 874. Nothing in sections 115.61 to 115.67 shall be construed as abrogating any statutory authority or responsibility of the Minnesota Pollution Control Agency. All territory annexed shall be subject to taxation by the district like other property within its boundaries for the support of its facilities and for the payment of principal and interest thereafter becoming due on its indebtedness, whether authorized or incurred before or after the annexation.