Gordon,
Having been to this movie myself....
The manufacturers do sell tanks that are "non food grade" but are food grade material - which is what you have as do I. Mine is a 60 gallon tank (which was twice the size of my TT's capacity when I originally bought it). put a 12v extension cord on the Live Well bait pump (Sureflo Livewell pirhana) to my truck connection for power and it transfers the water from the truck to 5er.
I looked at a better pump but realized that it's only moving the water downhill, so gravity would suffice but not fast nor efficient.
If I was going to do it again, I would probably go with a collapsible unit and use the pump. As someone already said, storing it is a pain, but since I've had mine for 12 years, it's not worth futzing with it.
What I can tell you is having the external water tank and the external gray water dump tank has saved all the complaining about not letting the water run - don't waste the water conversation. While it may take me some time to fill up and drain, it has made being out in the wilderness much more satisfying for the family.
I know you'll be much happier not having to move the TT everytime you need water.
FWIW, I also took a bilge pump and connect it the sewer connection (via the hose fitting on the sewer hose cap) and pump my gray water into my gray water tank so I drain out the gray when I need to fill with fresh. I had to imagineer a bilge pump into in/out via hose fittings.
Josh