A plumbing end cap that is designed to assist a plumber in removing the air in an underground piping system just prior to testing the system with water. The end cap includes a small valve stem that is fixedly attached to the end cap prior to the end cap being attached to the terminal end of an open pipe. The end cap allows a plumber to eliminate the need to retest a closed system for leaks in the event the water level drops during such a test, due to air remaining in the closed system.