It’s not heavily recommended to entomb pipes at all, but there are times it simply has to be done. Remember, that concrete gets violently hot. You’re going to need to keep the pipes cooler when pouring that concrete, and we do it by keeping water flowing through the pipes as it’s being poured. We see this in new construction often, when the spa or pool is finished and they have to dice it up to replace pipes.
Check out this video where we got to a spa in Malibu that had to be torn out and pipes had to be replaced. The deformed, warped and shrunken PVC was the result of hot concrete.