Most guys have the vent coming out of the bottom of the plane. When you disconnect it some residual fuel in the line comes out. I put my vents coming out the side of the fuse as close to the bottom as I can get. Since the vent line is horizontal and there is a slight suction on it no fuel or never more than a drop comes out when you disconnect, and even if some does your hand isn't under it.

Another good reason to put the vent on the side is if you ever have to do gear up landing you won't rip it out of the fuse.

Also I always place the overflow tank on the ground before disconnecting.

Joe