I set mine up for 2 lines. One line is a simple vent that I run out the bottom of the fuselage. The other line has a "T" in it at a location that lets me add a side line to a fuel dot somewhere on the front of the fuselage. Put another way, the line to the carb is also the fill line through the "T".

As far as preventing leaks while inverted, the carb suction pretty much eliminates that. What it doesn't prevent is negligible. Nice thing about gassers, you can put the tank darn near anywhere.

Make sure you are using stoppers and fuel lines for gas, not glow.