got the idea from kevin green, here is what he said about it, > I bought a package of Dubro fuel can fittings. (The ones that enable you to convert a container top into a fuel can top.) There is one brass piece in the package that has threads in the middle and barbed nipples on each end. Take this piece and two brass nuts and put them aside.

Get a drill that will enable the brass piece to pass through the fuselage and drill a hole where you desire the vent to exit. Get a thin piece of ply (1/16" works well here) and glue it to the inside of the fuse, centering it over the hole you just drilled. When the glue has cured (I used Flex Zap) drill through the ply with the same drill you used earlier.

Get the brass fitting and the nuts---Put thread locker on the threads of the brass fitting and thread one nut onto the brass fitting, stopping not quite half way to allow for the thickness of the fuselage and the ply backing plate. Place the brass fitting with the one nut secured with thread locker into the hole you drilled, accessing from the inside of the plane. Put thread locker on the brass fitting and then thread the other nut onto the fitting from the exterior of the plane. Tighten the nut snugly against the fuselage.

There you have it---A nice fitting that does THREE things!!!
#1) Obviously, a vent and overflow for fuel tank.
#2) The nipple on the exterior will allow you to connect a ground run tank that also serves as an overflow container to catch excess fuel that is vented out during refueling. (I don't waste a drop!!!)
#3) The nipple will allow you to connect a plug made from a piece of fuel line and a Great Planes fuel plug. (The Great Planes fuel plug is the same plug that BVM uses with the UAT.) This will seal the system and help to prevent fuel spillage and fuel vapors from stinking up your transport vehicle.

I like doing the vent this way as it is very secure and won't get lost inside of the fuselage or won't get pinched off in the airflow. Also, I like the three benefits as described above. I use the large Tygon tubing to connect the tank to the vent fitting.