Quote Originally Posted by elsie View Post
John, if the main drain's function is as a source of water for the pump, where's the source of water if that drain is closed/covered/never opened? Why even have one? It's clearly not pulling water from the pool. I thought the pump recirculates water via the skimmer pvc and the returns?
Water is drawn into the pump from the skimmer(s) and the main drain and sent back to the pool through the returns in a typical pool installation. I'm not sure why a main drain would be installed if it wasn't opened, but it is fairly common to cap one if it starts to leak. Their only function is to provide water to the pump except in gunite pools where they also have a hydrostatic relief valve to relieve external water pressure when the pool is empty.