The fresh water tank (the only tank in the COMET - no grey or black water tanks) lives underneath the rear couch/bed.
Originally it was under the dinette bench on the port side, but that meant that there was about 15 feet of tubing wrapping around the entire trailer to get from the tank to the faucet on the other side.
We moved it to underneath the rear bench to be closer to the faucet. The fresh water tank is 15 gallons and I refill it about every 3-4 days. You don't really use a lot of water when you have to pump it by hand. And the hot water is just one of those black bag camp showers that I hang up outside.
Here's how we installed the new fresh water tank.
Now, we actually installed the kitchen before attaching the water tank and hooking everything up, so that's where I'll stop for now.
Basically, the tank got put into it's spot under the bench, it fit very snugly. We hooked up the fill line to the appropriate fitting that we had installed in the side of the tank, and the air vent line to the appropriate fitting.
We put the fitting (barbed) into the bottom for the faucet line as well, but didn't hook it up until the kitchen was finished. So we'll look at the kitchen then get back to finishing up the water tank.