Always full . Many times the water at campsites tastes weird to me . Think about it , why have a forty gallon tank if you are not going to use it . Carrying 20 or 30 extra gallons will weigh no more than your wife or two big dogs . Your truck and trailer will weigh 13 or 14 thousand pounds , do you really think 150 lbs of water will make any difference . SORRY for the rant , my brother weighs himself over three hundred pounds and he will not fill his water tank . I keep telling him to loose half his weight and fill his water tank !