New Fuel Tank / Seal yet massive Leak after filling my Tank

I had this exact problem with my Dart when I finally put it on the street after my build. It turned out that when the filler neck was pushed into the tank, through the seal, it pinched and split the bottom of the seal leaving essentially a nice size hole for gas to pour out of. I eventually pulled the neck and old seal out and installed a new seal. The trick to getting the new seal into the tank is to boil the grommet for a few minutes first and then it should pop right in the tank. Then take a generous amount of dielectric grease and lube up the outside of the seal and the filler neck should push right through without resistance.