Neither the commission nor any of the counties, cities or towns in whole or in part embraced within the district shall have power to mortgage, pledge, encumber or otherwise dispose of any part of the sewage disposal system of a commission, except such part or parts thereof as may be no longer necessary for the purposes of the commission, whether the same shall originally have been acquired by such commission or by one of the counties, cities or towns. The provisions of this section shall be deemed to constitute a contract with the holders of the bonds of the commission. The sewage disposal system of a commission shall be exempt from any and all liability which may be incurred by, or imposed upon, the commission, or any county, city or town, which, in whole or in part, constitutes any part of any district.

However, a commission may sell, lease as lessor, transfer, or dispose of all or any of its property and facilities in such a manner and upon such terms as the commission may determine to be in the best interest of the district, on the condition that the commission meet and discharge all of the requirements of the bonds issued by the commission, together with all principal, interest, costs and expenses.