It may depend on the exact chemical formula of the pvc. I have come to suspect that they are not all created equal.
I still remember the conversation some 25 years ago. There was no internet as we know it today and little industry training. I had been an electrician before so had no experience with flex but plenty with pvc and had several spa plumbing repairs blow apart at my first job in the business. So I called the flex manufacturer. Had to leave a message and wait a few days for the guy to call, but he did. I explained my situation, he said "Are you using primer on the flex?", I said "Of course.", he said "Well DON'T!", and hung up the phone.
Ahh, the good old days...
So I have not used primer on flex since. And I swear by Christys.
Contractor preferred, premium formulation Medium body, very fast set All classes and Schedules thru 6″ diameter interference fit (Schedule 80 through 4″) Can be used without primer if local codes permit for non-pressure systems up to 6″ and pressure systems below 4″ Blue in color
tchristy.com