I really appreciate the feedback, Yes, I had the feeling it would be about impossible, but thought perhaps someone else had success with replacing their pipes, with this method. I hate the thought of digging everything back up again, especially since I had to locate and tunnel under a propane line, and a drain tile from the house the first time. I'm sure if I try to use a trencher I'm going to snag the old line, and then really have a mess. The next time I will plan on running the 4 in. inside of a larger drain tile, either 6 in. or 8 in. I don't know what brand this Pex is but I ordered it from Brent Industries in NY. It is supposed to have a limited lifetime warranty, and have e-mailed them for the specifics of the warranty, so far no reply after 2 weeks. I have read about some failures with the crosslinking process on this orange pex-AL-pex. Anyone else hear of this??
I also have a run of this pipe to my shop, keeping my fingers crossed it holds together!!