Pool pumps & filters are quite low pressure things even on 2" so don`t see why you struggle.
You tried these?
Mega Union coupler | Bosta UK Ltd
Come threaded for plastic or metal pipes or solvent weld
Yes we use hundreds of those a year. Fantastic as the seal is perfect each time and allows components to be switched out in moments, tool free. But sadly the pump/filter ports themselves are threaded, so threaded seal connections still exist in the system. We don't struggle so much with the pool kit really though. But when we have 3000 solenoids all with threads going into a single distribution manifold, all of which have to be (and remain) leak free, even a 99% success rate would mean 3 leaks per assembly. So that's why we're looking for quick and foolproof sealants to use.