Fuel Cap Breather

[joebloggs]

Been looking around the internet and not found much, but was wondering if there's a  breather vent or hole that can be cleaned or poked on the fuel tank cap at all?

Is the tank not vented from underneath, when I cut the bottom of the tank out I seem to remember two brass/copper tubes connected from the bottom to the pressing that the fuel cap bolts to, I guess one is the overflow and the other the vent.