I only empty my tank when I winterize it. Some people don't like to carry full tanks. I don't mind after six years I haven't seen any noticeable difference in mpg full or empty.
I keep the tank topped off as you never know what the water will be like at your next stop. Get into an area where the water is hard and you'll know what I mean. I've even been places where the water has a sulfur smell. No thanks, I'll carry my own water.
Tony & Ruth........... FMCA#F416727
Newmar Dutch Star 4320, Spartan MM Chassis, Cat C9, Jeep Grand Cherokee,with Hemi, hooked up with a Blue Ox Aventa LX, and Brake Buddy.