Hi

Recommend you get rid of the third line and use only a tank (preferably Hayes which eliminates bung plug problems) with a upper vent line and a clunk line. Also suggest you plumb your engine exactly as indicated in the YS drawing that scale for me posted above with one exception. That suggestion is to add two tee's to each line making sure the tee on the vent line is on the tank side of the check valve Now two short pieces of fuel line is added to each tee enough to protrude below the fuselage a tad in the cowlings air outlet hole at the bottom. both of these lines are plugged with a line plug.

Fueling is done by first removing only the plug in the vent line (notice in my picture one of the plugs is painted red) If you remove the clunk line first that will allow residual pressure in the tank to squirt fuel all over you. After the vent line is unplugged and the pressure has vented you now fuel from the other line (clunk line) and when full it will shoot out the unplugged vent line. After fueling it is important to replug both lines.

Also notice in my picture it shows how to use filament tape to reinforce the tank.

John