Personally, I would NEVER use anything but Schedule 40 or higher on a pool. Schedule 40 is designed to be pressurized, regular is not, and is for household drains and such that use gravity. If your fitting and/or pipe is not Sched 40, that's probably why it's leaking. Or it just wasn't taped properly when it was assembled, in which case disassembling it and re-assembling properly should fix it.

Sched 40 PVC and fittings are incredibly easy to work with and should not leak. I use both hard and flexible piping, where the flexible is called TigerFlex. Too many installers use TigerFlex with internal barbed fittings and hose clamps and then it leaks. You should use glue-on fittings instead and then it never leaks.

Good luck!

Carl