I decided to try a uni-flow tank, and decided to omit the third line used for filling, and figured I'd just unplug the carb line and fill there. Well, I tried that, but the fuel went straight into the muffler. And NO it's not a plumbing problem, all lines are properly hooked up, except of course the filling line.

So why is the fuel going into the tank, and right out to the muffler?
Will adding a fill line fix this?
How would I fix this?