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?

the only reason for that is the line goingto the arb is in the middl and the muffler line is lower than that, the muffler line needs to be up away from the bottom of the tank, it needs to be as high in the tank as possible so that the fuel reaches it last as the the tank is completly full