I agree with the above. I use hand drill for holes I tap all the time. You don't NEED a drill press but it is alot easier. Give it a shot, its only a plug.
On the other hand, I do see this as being a critical application (is it really at 300psi?

), so I understand your concern. I'd be glad to tap that M20 plug if you would like. Let me know. I only have an M10x1.5 tap though, no 1.0.
Lastly, why are you all giving bmwpower such a hard time? He didn't ask for other ways to get a temp sender in, he asked for help tapping a hole.