[parsonsj]

It's a good question, and the video is a bit confusing on that point.

All fuel tanks need a vent, return line or not, to allow for filling up the tank, for replacing gasoline with air as the gas level drops, and for temporary conditions such as fuel displacement during vehicle maneuvers or heat absorption (as mentioned in the video).

Most older cars use the cap as a vent. That was fine in the sixties, when nobody really cared about gasoline spillage or odor during storage. That's no longer cool, and modern cars use what we call a non-vented cap (though they still have failsafe vents in case of extreme pressure buildup), along with a fuel purge system that allows the tank to breathe for those same reasons.

If you want to use a modern fuel cap, and reduce fuel spillage and odor, but don't want to install a complete fuel purging system, that's where our vent comes in.

Cut a single hole, fasten it in place with the bulkhead nut and environmental seal, and connect the tank vent port to our vent.

Hope that answers your question.