12. (1) The municipalities which adopt a resolution under section 3, or any of them, may agree together to carry out together the work mentioned in the said section 3 and exercise together the rights conferred under section 6.
(2) The municipalities which avail themselves of the provisions of subsection 1 must each adopt a uniform resolution for such purpose and submit it to the qualified voters for approval.
(3) The apportionment of the expenses necessitated for the carrying out in common of the work and the exercising in common of the above mentioned rights shall be effected under an agreement entered into between the municipalities concerned, and, failing such agreement, according as the Board may determine.