I like three lines with two clunks in the tank - - one for fuel pickup (to the carb) and the other to your fuel dot. But, Ihave never tried a 2-line, so maybe I'll have to. With glow engines (in a 2-line situation) I'd worry about pumping fuel into the carb while fueling through your T. I guess you don't have that concern with a gas engine because fuel will not flow into the carb if the engine isn't running (?).