Gas tank vent issue

[shrimpman steve]

Ok, here we go. In the past as I was coming close to a full tank while fueling some gas would spit out of the vent nipple on the side of the boat the last couple of times I filled it, no warning from the vent and fuel back sprayed from the fill hole all over me. Next thing I noticed was a bulging fuel tank. So much so that it popped the fuel tank access hatch on the deck. I figured it must be a clog in the vent hose. I disconnected the vent hose from the tank and blew thru the hose, no clog. Reassembled and have the same problem. When I filled it yesterday before launching same thing. Got soaked in gas when the tank got to full and noticed the deck hatch popping up again. I though I would relieve the excess pressure in the tank by taking off the fill cap, but when I did no escaping vapors. After running for 10 minutes the catch cover in the deck was flush again. Boat is running fine but I obviously have a venting problem. I'm afraid the tank will split if it swells like that.

Help.