The plaster crew is coming today to spray the pool, and since the pool is empty and prepped, I am taking the opportunity to replace all of the jet nozzles and removable fittings with brand new stuff (the previous owner let the water balance go out of hand and stained a lot of the plumbing). I've got everything else, but I can't figure out what this item is called so I can get one. It sits about a foot and a half below the skimmer, and seems to have some light suction to it. I was told by one of the service crews that it is for if the water level gets below the skimmer to stop the pump from sucking air...