[Fishin2dMax]

I had the exact same issue on my 305 RL. On some trips here in the Rocky mountains, I would lose up to 1/2 a tank of freshwater through the side vent. At one point, I decided to change the side vent to a gravity feed inlet to fill the tank and just close the cap while traveling; however, that method was way too slow to fill the tank, so I now use a 12 volt portable water pump to fill the freshwater when boondocking. I also decided against closing the cap on the vent tank since the risk is too high of forgetting to open it and blowing the tank while filling.

To reduce the water splash issue from the side vent when traveling, I added more vent tubing and raised the tank vent line up to the floor level and back down to the skirt side vent / inlet (make sure line is straight sloped for drainage and doesn't trap water). To do this, remove the few screws holding the side skirt at the bottom and rear of skirt and you will have just enough access to add approx. 6" of hose to reach the bottom of floor (use a PVC pipe mount) and slope back line down to side vent in the skirt. This rise of approx 6" will make a difference in the amount of water that is lost through the rear vent while traveling (won't totally eliminate on hard turns). You may be able to stretch the existing vent hose line up to the floor level, and back down, but I didn't want to risk breaking the line.

Another fresh water tank issue that I, and others, are experiencing is not being to access a significant portion of the water of the tank from the water pump. I still have 12 to 13 gallons of water left in the tank after the water pump can't pull anymore out? I'm still looking for a solution to this issue.