Mitch:
I use this tank on my profiles. You have the tubes correctly named. The tube on the front goes to the engine, top tube is fill and bottom is overflow. I connect the overflow to the muffler using standard size silicon tubing, and then to keep pressure in the tank, I cap the fill tube. You can cut a short piece of silicon tube and plug one end with a piece of metal rod. This can become your fill tube cap.  If you don't cap the fill tube , with the tank pressurized by the muffler, the fuel will be forced out of the tank. So you have to cap the fill tube. This seems to work good for me. You may want to un-plug the muffler silicon tube when you fill the tank. Otherwise, when the tank fills the overflow fuel will drain into your muffler. This can cause your engine to become flooded. Makes for a problem starting. Once you see the fuel coming out of the overflow tube, stop filling, then attach the overflow tubing to the muffler. Cap the fill tube and start the engine.
Great thing about this web site is all the excellent knowledge out there. These guys have really helped me. I flew c/l back in the 60's and now back into it. This site is very valuable and worth a small donation to keep it going.
Jim