Originally Posted by Venice Motor Bikes
I've done plenty of these in frame tanks... Just drill & tap the frame for the petcock; you should also use some gas proof thread sealer on it.
As I said, I know it is overkill, but I like the extra security overkill offers. One less thing to worry about. I have more than a few years building/tuning USAC sprint cars under my belt. I grew up in a body shop doing custom cars, bikes and collision repair. I will trust a 1/2" of threads over an 1/8" any day. I don't suggest doing this on a bike you want to save the factory paint on though.