Interesting, but hard to believe, as Sched 40 pipe is used for water supply under pressure everywhere. Might be an interesting experiment though. Those "vapor barrier" bags are interesting, do not know the tech behind them or what they are designed to prevent.
I gotta say, I was hoping for gold or maybe diamonds or something. Ammo was the last thing I expected. Retrospectively, it should not have been. I,too, was surprised. I can tell you with certainty that a packed in grease, sealed PVC pipe will not hold up for even a year or two in salt water. Fresh water, I don’t know but I would not put a $500 AR or whatever into a test of it. Folks that buried stuff back when BJ and Monica were in office may consider checking on their stuff. It may not be worth much anymore.