My 25RR Grey Wolf would read full and burp at 2/3. Make sure you're level when filling the fresh water tank. If you lean in the direction of the fill tube or the overflow/vent you can give up a lot capacity. When it seems full due to it backing up in the fill tube or coming out of the overflow underneath, give it a minute and then try adding more at a slower rate (Close the spigot halfway).
We carry drinking water for taste, even though we filter because we do use the tank water for cooking, ice cubes, and teeth brushing etc. But you should easily get a couple of days more based on the recommendations here as long as your tank is full, even if you do use it for drinking.
Rig: '16 XLR Hyper-Lite 29 HFS > 2014 Nissan Titan Pro4X 5.6L
Toys: '08 HD Screaming Nemo Ultra > '07 HD Dyna Street Dori
Family: DH - JC, DW - Malinda, DD - Sparky the Wonder Chug (Chihuahua & Pug)
Days Camped: 2016 - 22 (+13 reserved); 2015 - 27; 2014 - 16