Hard to diagnose without a picture, but is this an above ground pool? I would think to be safe you could use some silicone. There is also a product I have used for my gunite pool where it connects to the skimmer, it is AquaMend underwater repair epoxy. I purchased it at home depot and it works great. It says it bonds to fiberglass, wood, metal, ceramics, concrete and many plastics. This might be worth a try also.