I'm a gonna get jumped for this, BUT, I'm definitely against a two line system...
Air bubbles, and dirt...[>:]

I'll vote for the three line fill..
One line to the carb with a chainsaw filter (felt type) on the other end in the tank for the clunk..
One vent line...out the bottom on the plane..
One fill line with a fuel dot plug..

My 2 cents worth.