Bill,
my MIL has said the same thing about water having a nasty taste. Not that she can swallow more than a couple of sips a few times a day, but even that she says is too much given the taste of it. What I might suggest is putting a small amount of juice (like 1/4 strength, or even less) so that it is very dilute, that would not only flavor the water a little bit, but would also give added nutrients to the water. There are lots of different things you could try to flavor it, even liquid ice tea mix! (I use that myself, it comes in raspberry, lemon and even peach).
As for water in the tube in order to get enough hydration, as far as I am concerned if you have the tube, use it for anything you dont care to put in your mouth! There are far worse things you could be doing than tubing your hydration...

I know lots of people who use it for hydration only (though most end up using pedialyte as it gives added benefits to prevent dehydration so long as you are not getting too much sodium etc....)
Has you tried taking in extra fiber, or using a formula with added fiber? that can also help with the constipation angle. My son uses a formula that has benefiber added to it (his formula actually is made from real food, chicken, cranberry juice, beans, peas, etc) and it has helped him.
I hope that helps, a little...
Heidi (Sean's mom and DIL to the bravest woman I know, oral cancer 6 yr survivor, esophageal 3 yr survivor, and recently re-diagnosed with oral)