Fresh Water Capacity on an RV typically includes the water in your water heater. That said, 65 gallons is still low. On mine, the tank never get to more that 7/8 or so full, because the fill pipe and the vent are located on the side of the tank. and the plumbing runs almost completely horizantal (flat) to the fill port, so any more that I try to foce in, just runs right back out....
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter