Asking to see if anyone knows what type of port this is - excuse the dirty pics of the pool wall, bought a house with an inground pool and still figuring out the equipment part. My pool has (3) return jets around the walls of the pool that appear to function normally pushing out a flow of water. In this photo, is a 4th "port" on the sidewall that only trickles out a low flow of water but I am entirely not sure what it is used for. It doesn't look I can fit an eyeball fitting in it like the other jets, so I'm just trying to figure out what it does. Anyone familiar? Thank you!