Yesterday, I decided to do what some suggested. For water availability during freeze out emergencies, I filled the fresh water tank. I've never put water in the fresh water tank because we've always had city water. So I turned the dail on the water control to "fill tank". Everything was working fine, could hear the water running. Tank was filling. Thinking it might take several minutes to fill it, I started looking for the over-flow port. Found two, at least I thought they were over-flow vents, cause they were near the rear, one on each side of the unit, near the tank. Next thing I know, my wife comes outside in a panic........the living room floor is raising up like a pillow "noticablly". So I quickly shut off the water. Look underneath and WOW!!! the tank had expanded well beyond full, and had pushed the spare tire rack down (bent the angle iron) and the living room floor was pushed up at leat 3-4", including the kitchen Island on one end. The tank didn't explode, but did turn into a big ball. I started draining the tank. The floor settled back down to level, but it did some permanent damage underneath to the spare tire rack and frame. Question, what could have caused this? shouldn't there be an overflow vent on this tank? if so, where is it? does it have a valve that has to be opened? I'm soooooo lucky the tank held the pressure. I hope nothing else is damaged.