Charles, several have suggested that the top, open end of the clear tube be connected into the top of the tank, or into the side of the filler neck. That is important to keep the top of the fuel indicator line and the vapor area at the top of the tank at the same pressure. Per the plans, the filler cap has a small, open tube that faces into the slip stream. When flying, this causes the pressure in the tank to be a bit higher than atmospheric pressure. If the top end of the fuel level tube is connected to the top vapor space of the tank, it will indicate accurately. If it is simply left open in a space at atmospheric pressure, the higher tank pressure may push fuel through the tube and out the top. It will not indicate accurately, and possibly be a safety issue.
I've seen fittings made for the plastic tanks that use some type of rubber grommet to seal penetration of the tank. That would work well, especially if you are connecting into the vapor space of the tank.
As far as the slope of the fuel line from the outlet of the tank, I made DE Stubby's lines to be running downhill (and also on our LEU Treehugger, RIP), even when at a climb angle. Other routings may work, but I don't think you can go wrong by sloping them down towards the engine.
Hope this clarifies.
