A coupling used during testing of a water line including an upstream pipe and a downstream pipe connected by the coupling. A removable barrier disk prevents water from flowing through the connected pipes until after testing, when the disk is then detached from the body member of the coupling. A piercing assembly interacts with a groove near the perimeter of the disk to initiate a tear that propagates along the groove as the disk is pulled away from the body member of the coupling. The piercing assembly is attached to the disk by a fulcrum element offset with respect to a center of the planar disk.