You can also go crazy and do the "Ultimate water transfer bridge" modification that some of us have done:
http://www.trailmanorowners.com/foru...ad.php?t=10458
I did that, plus added a hose port onto the hot water heater drain. This lets me fill both hot and cold sides with the shells closed (albeit longer than it takes some going through the fresh drain). It also allows very easy filling of the tank when empty, without needed to lift and pour anything, using the on-board pump.
There's a 'hidden' mode if you choose this route, one that needs an addition to the bridge, that will allow you to use any tank in place of the on-board tank. So, you can fill one of those large 40 gal bladders, and then use that directly without having to transfer the water first. I didn't do this mod, because (a) I thought of it later, and (b) I don't have a case-use need for it. But, someone with, say, an on-demand hot water heater, who is camping without water hookups, might want a large bladder as a water tank, and this is possible.
Just letting you know all the options!