Jadnashua
Retired Defense Industry Engineer xxx
There's a lot of materials science that goes into the rules. Stock PVC drainage pipe is not rated for long-term external UV exposure. There are lots of ways to make pvc from the density (some pipe is specifically lighter - it has air bubbles inside), UV resistance, heat stability, and probably other things as well. What you do for yourself is one thing (although if there was any eventual property or personal damage/injury caused by it, your insurance company may refuse to pay up), what you do with others, even if you give them away is risky. Whether you believe it or not is irrelevant.