"Photo one is my constant companion, mascot, and trusted advisor. A recent SB for the RV12 adds a vent to the fuel tank to help control overfilling splashes. They offered a bulkhead fitting (where you have to take the tank apart to tighten the nut on the bottom). I have no faith in such fittings for this use, so will use a riveted flange like this one in photo three.. A friend suggested that putting on TWO of them would allow future expansion of aux fuel tank input to the main tank! Great idea, so I will have two of them on the top of my tank. I modify these a little bit in the lathe to make it easier to rivet to the tank, see photo 2."