3 lines is the way to go (fill/dot, vent and carb).
A simple "T" in a two line system won't work as you mentioned.
The only way to use a two line tank is to use a fuel filler valve which goes in between your tank and carb. When you plug in the filler connector, it blocks fuel from going into the carb but allows it to flow back into the tank (while the vent line simply vents).

I no longer use these filler valves as they tend to fail at the wrong times. They also are notorious for lean running engines as they tend to leak over time, allowing air in to the carb. Best bet is a direct line from tank to carb (filter is optional... I do not use them as I filter the fuel when filling up the tank.. just one less thing to go wrong in my book)