Which gas tank?

The vapor return, while a good idea, has nothing to do with a tank vent

There's no such thing as "somewhat vented." The late model "pressure vacuum" caps were NEVER intended to be a "somewhat vent" and can allow the tank to operate under a slight vacuum, which can cause vapor lock !!!! or a slight pressure

Vented cap? I guess if you don't mind fuel all over the side of your car...........................

So please tell my, clhyer, how IS your tank venting? You say "don't plug the vent nipple" OK, if you leave it open (at the tank) it WILL leak.