It's good to have some sort of loop in the vent line, similar to the picture in post #1. It's not unusual for a little bit of fuel to get into the vent line during loops, rolls, etc. Once the plane rights itself fuel in the horizontal section of the vent line will migrate back to the tank.

I also put a forward facing bevel at the end of the vent tube to create a bit of positive pressure to help keep fuel from exiting.

Joe