Mysterious air bubbles coming into filter basket, cannot figure out how


Active member
Jul 10, 2015
Hello all,

I recently had some work done on my pool:

- New vinyl liner
- Above ground plumbing around filter redone
- Leak underground fixed in one of the suction lines.

I've always had some air bubbles in the basket near the pump motor but now it seems to be more.

Please see the attached picture for reference. Pipes 1 and 2 are the suction lines, which go into pipe 3 via a control valve and into the basket with the motor, up through the clear pipe #4 into the multivalve port and into the DE filter. What happens is that after I stop the filter, in about 20-30 minutes I see a slow trickle of air bubbles (maybe 1-2 every 30 seconds to 1 minute) coming from the section where pipe 3 attaches - and it always takes roughly 20-30 min, until then it is fine. I first thought it was the gasket so I put in a new one and lubed it but no help. Within an hour or 2, the water in the little basket has dropped maybe an inch or 2 to where I think it is below pipe 3. After this hour or 2 I can still start the filter and within 30 seconds it seems to prime itself and go but this is all recent so I haven't had a chance to let it stop overnight yet.

Aside from the gasket, conceptually I don't understand how pipe 3 would be introducing air bubbles into the basket. Even when I use the valve between pipes 1 and 2 to shut them off entirely, I still see air bubbles, so I don't think they are coming from the underground lines. I also don't see any above ground leaks anywhere on the suction side. I just don't get how pipe 3 would empty out with air - is pipe 4 pushing down on it? It seems to stay full.

Does anyone have any ideas? I'm totally baffled.


Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
I would take a close look at the filter, specifically the psi gauge/air relief at the top and perhaps the band clamp. Sometimes you won't see water leaking out, but when the system is off those areas will let air "in" and cause water to shift around a bit once the system is turned off. All it takes is a tiny O-ring to wear or get dry (lube).