guess I
have to vent tank,harpoon it now! tanks only have the small roll over vent now.
No need to put another hole in the tank, just remove that factory roll-over valve and use it for a vent, putting a large fitting and hose onto it. It is tight up there, so you need a elbow that fits right into the grommet.
The other poster and where he punched a hole beside the large fill nipple in the tank is the way GM does it. And then they run this 1/2 hose up to a fitting on the filler pipe, just like some others are doing. They key to this is install the 1/2" vent pipe into the filler near the top, so when you insert the station nozzle, the tip of the nozzle where the fuel comes out is PAST the vent pipe fitting. This will keep the turbulence from the vent away from the fuel going in.