ok here is one i know someone can help with, sunnybrook titan 39ft toyhauler fifth wheel,, the factory tell me this unit has a 60 gallon fresh water tank,,,,, now i put water in from my 55 gallon drum we have for dry camping,,, when the tank is full it only takes 25 gallons plus 10 gallons for the hot water heater plus i figure 5 gallons for all the lines,,, then i empty the fresh water tank using the rv pump back into my 55 gallon drum which is empty, the tank runs dry after 25 gallons, i guess my question is do i have a 25 gallon fresh water tank or is something not letting me get all the water in the tank,,,, next step woul be to undo the bottom skin of the rv to physically see how big the tank is,,,,, it is not taking 50 or 60 gallons,,,, hope this is not to confusing, thanks