If I use a single hole I make it so the lines just fit through then use silicone to plug it up and keep the fuel mist from getting into it and soaking inside the fuse. I used the clear plastic once that comes in the tank kit. When I tightened the bung it compressed the plastic tubes and almost closed them off. From then on I only use the brass that comes with the tank kit. I usually do as eddie and drill two holes in the fire wall just slightly bigger then the fuel line. Either was works though, just a choice thing.