My equipment is old but I have only owned the house for two years. Last year I replaced the multi-port valve with this (Top Mount Thread-Praher (tm-12-a) - INYOPools.com
All worked well last year.
Starting this year (after winter), there is constantly air in my return. I have to prime the pump before I start it as the water drains from the pump overnight.
I removed the multi-port and the o-ring is perfect. I cleaned off anything that I thought could be an issue. I reinstalled the multi-port and added teflon tape and added new piping from the ground up.
Still there is air in the line and lose of suction each morning.
I noticed a soft spot on my sand filter that stays wet.
Occasionally I still see a few drops of water where the multi-port and filter meet.
Sometimes, not often, when I shut off the pump there are a lot of air bubbles that rush back to the skimmer basket. Enough to move around the basket and cover.
Water level is an inch below the top of the skimmer face.
The o-lid around the basket lid has been replaced. I did not replace the lid as it appears to be fine.
What does this sound like to you? What would be your next step? The multi-port is on very tight. More tape or should I try something else?