A system and method for determining the reliability of at least one communication link between nodes in an ad-hoc communication network. A valve assembly is disposed in the cavity through the opening. Each container has a base on the shelf, upstanding front and rear walls and upstanding side walls with the front and rear walls inclined at a wall angle to a plane at right angles to the base the base so that with the base sitting on the inclined shelf the front and rear walls stand substantially upright.