This is my 3rd year owning a pool and I never noticed it before. Everything appears to be working fine but when I turn my pump off o can hear air coming from the waste output. I put my hand over it and confirm air is being sucked in. Maybe a bad seal in the multi port valve? Since it doesn’t appear to be appear to be effecting anything I wasn’t sure if it was worth the time to take that apart. It’s not a lot of suction but if i cover it with my hand I can feel suction start after about 6 seconds. I could put a cap or something over it until I need to use the waste line but wasn’t even sure it was an issue