Camec water fillers

Calling all Adventure offroad camper trailer owners (or anyone who knows about water fillers). I need your help. Our Adventure lost the inside of the water filler (not just the cap) off the camper on heavy corrigations and Camec dont make the screw type water filler anymore so we replaced it with the new version which has a hinged door instead of the screw cap. Has anyone had to replace their water filler complete unit (not just the screw cap). The new version is flawed and allows water to return up the breather hose and fill the cavity underneath as their "breather" is just a hole in the breather pipe which as well as letting air in to pressurize the tank, it also lets water out when you fill it up funny enough. The old version sucked air in through the screw cap and didn't have this little hole in the breather pipe. If you seal the hole on the new one, the door certainly seals tight and sucked the tank in. Camec have been less than helpful to say the least. We have tried fitting a one way valve that camec supplied additionally but they either arent sensitive enough to open when needed or lets water escape through it still. Has anyone solved this problem or do you know a different brand with the same mounting holes and has the breather tube hole protected from dust (as some brands breather hole is exposed to dust if you look carefully).