Oh my, I feel like such an idiot! Dave, I just went out to check, and yes - on waste I can feel a lot of pressure coming back into the pool. There is some on backwash, but not as much. Duh, why didn't I simply stick my hand in front of the return jet two months ago????? We couldn't see any water coming back in, or at least didn't notice it.

So, what to do to fix this? Is it a spider gasket? My tank is just 2 or 3 years old.

Thanks so much!