What adhesive would mate PLA and PVC?
Beware that if in a use that is subject to plumbing code, your 3D printed item almost certainly will be a code violation.

The probable best bet (and I'm not guaranteeing success) would be a "Multipurpose plastic pipe glue" - go to the plumbing section, find the PVC pipe cement, don't buy that - look for the somewhat smaller stock of pipe cement that claims to work on PVC, ABS, and perhaps a few other variants of plastics - try that. Use PVC pipe cleaner and primer on the PVC side of the joint. Make some test joints and try to tear them apart after they have had a day or two to cure.

If, as I vaguely gather, PLA is essentially the most common form of hot glue, then judicious and careful use of a hot glue gun would be the other option that might work.