Need suggestions for venting my fuel tank

My cap does have a hole in it, but if you blow or suck on it, no air flows through. I originally hoped that I could drill it out and open it up to make it a vented cap, all problems solved, vent at the highest point on the fuel system. I don't know what that hole is for, but at least on mine, it is not fuctioning as a vent.

http://mmb.maverick.to/attachment.php?attachmentid=14068

Ended up doing the hose at the top of the tank.