I may be how your fill tube and vent tube are connected into the FW tank. Mine, for example, is routed into the side of the top and they're right next to each other. If I fill too fast, the turbulence and volume don't allow the air to escape and a bubble gets trapped in the tank. When I remove the hose, water literally shoots out of the fill pipe, venting the tank. If I fill slower, it seems to take more water and not shoot it back out. My bigger complaint is the drain and pickup tubes are not on the bottom of the tank, they're in the lower corner on the side, so I have about 1 1/2" of water that I can't access. Probably like 7 -10 gals. Don't know why they do that. It never drains completely.
