Bill,
I have been slow moving on this as life has been very busy. I have however learned of this idea using a brass compression fitting. Inside the stock fitting on the compression side is a stop so the copper tube won't go all the way through. What I did was to set the fitting up on my drill press and drill that stop out, and also continuing drilling out all the rest of the way through the fitting and out the 3/4" NPT side (the side that screws into the tank) with a 5/8" bit, which is the OD of 1/2" copper pipe. The brass drills very easily. I need to show this to my plummer to make sure there will be no leaking issues doing this. The beauty of the compression fitting idea (if it works) is that the bent siphon tube can be slipped in to the tank and allowed to rest at or near the bottom. The tube would not have to be straight up and down, but could just lay on the tank bottom at an angle, that way measuring the length is not so critical. Then the 3/4"NPT side of the fitting can be screwed in to the tank bung, the tube being still free to turn at this point. Then, when all looked good, the compression nut would be tightened down, locking everything in place. Then reattach the pex supply to the copper and you're good to go. What worries me is the very limited space under there to work and get wrenches in, etc. To do this at the factory would take no time at all! I really want a plummer to check this out before I commit. Trying to avoid the can of worms if I can!
I also tried using a nylon fitting with a pex tube glued into the NPT side with JB Weld plastic epoxy. But this test failed the glue test. No surprise as pex is impossible to glue so I have been told.
I will pursue this and post pics as soon as I can. Hope to talk to Tommy Staggs again this week to make sure the 1/2" copper tube will fit through the bung. Otherwise I'll have to step it down to 3/8" copper and use a comp. fitting configured for that size.
Dave