If you don't boon dock, You really don't need to carry but a few gallons of fresh water for flushing on the road. My dealer filled mine up and I figured I was toting over 500 lbs of water. Drained it all but a little. My valve is behind the door side wheels.
2011 351RLTS Eagle, Mor/Ryde suspension & pin box
06 F350 PSD, SRW, LB, CC, 16K DrawTite hitch, Timbrens, TST TPMS
"Wag more, Bark less"