Two or more townships may exercise jointly the powers herein conferred upon each by this act; such joint exercise of powers shall be by means of a resolution adopted by the township board of each township, which shall contain the terms of the contract under which they proposed to exercise such powers jointly. The contract shall specify the respective interest and participation of each township in the acquisition of land; erection, operation and maintenance of buildings and equipment and which contain the rules and regulations governing the use of such land in disposing of garbage and trash thereon; such contract shall also define the respective interests of the townships in the proceeds from any sale or lease of the land. The joint resolution of each township board may alter or amend said contract in any particular.