I was re-reading these posts and checked out the links posted and read the documentation. It seems to me that all of the documentation is referring to the water supply system that is under pressure. It makes sense that leaks may occur if the system is under pressure. But what is the problem with using the cpvc fitting labeled "cold water only" on the TPR valve. The cpvc is still rated for hot water and the system is not under pressure so leaks are not an issue. I found the same fitting on another water tank today. The home was a manufactured home. I suspect there are a gazillion of these things attached to water tanks and probably no problems.

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Greg Jenkins