Re: fuel tank vent
Does your tank have two little pins that get pushed in when you connect the hose? One of those pins is the fuel shut-off valve and the other is the vent. So plugging on the hose vents it, and there is no vent in the cap.
Now: The rest of the story. It is a one way vent, meaning it allows air to enter the tank to replace fuel drawn out, but it does not allow air to escape, hence the pressure build-up. That feature is so fuel won't slop out the vent. I do think it may have an over-pressure relief valve that vents it before it blows up.
