I was told since some of my water supply system will be under where someone might occasionally drive, I should use Sched 80 pvc. Man at the piping supply store said it's fine to use sched 40 fittings (couplings, elbows, etc) with Sched 80. I know they fit together, but would it defeat the purpose of using Sched 80 pipe or be a code violation if I used Sched 40 fittings? Thanks.

I know they fit together, but would it defeat the purpose of using Sched 80 pipe
Well kind of! Schedule #40 fittings have thinner walls so if the line's going to be under much pressure I'd use the #80 fittings. To learn more click on; Schedule 80 versus Schedule 40 PVC Pipes and Fittings (http://www.squidoo.com/Schedule40vsSchedule80) Good luck, Tom

Thanks!