This drain nipple screws into the front (suction cover) of most Wavemaster Jet Pumps as well as the Sta-Rite 1Hp & 2Hp jet pumps. The function of this nipple is to provide a place for the 1/4" vinyl tube to connect onto the suction side of the jet pump then over to the heating/circulation pumps plumbing. The purpose of this "connection" is to prime the heater/circulation pump by immediately activating the jet pump once the spa has been powered up after a refill. The 1/4" tubing acts like a straw that sucks out the accumulated air from the heater, circulation pump and related plumbing enabling it to quickly fill with water to prevent a "dry fire".