Our external vent is a great addition to your new FuelCel fuel tank. It removes the venting from the cap which is the typical path for makeup air in the tank. The external vent is placed forward and to the left of the front of the tank in the form of a 6mm barb fitting. This allows for a catch can to be used for racing applications where rapid accelerations could send raw fuel out the vent. It also eliminates fume build up under a tank bag which could affect the paint or tank bag over time.