I don't think it goes to the bottom but I did read where it should be below the top of the fuel level. I guess that means to the bottom if running a low tank of fuel...
I saw a guy weld a patch on a fuel tank while the car was on a lift and the tank was full of fuel. While he was welding, fuel fell in flaming drops. "Just don't try this on a nearly empty tank," he said. That said, drilling into a cleaned, empty tank on the bench should be fine. My worry would be that I would drill the hole wreck the tank.
