CVelectric,
I agree with hbiss, but before I drill through rafters with one of those long bits, I would make a small hole with a long thin screwdriver along side of the rafter. I would then stick the screwdriver ( Or a piece of wire) inside of the hole to make sure that there was no pipes, or wire runing alongside the next rafter. Once I knew that the path was clear, then I would drill the hole. You might have to patch up several small holes alongside each roof rafter ( or floor joist) but it is well worth patching a very tiny small hole then drilling through a large waste pipe.
