On Thu, 25 Aug 2005 20:24:29 -0700, DaveC wrote:

I've got an old 20 gal (?) compressor tank in which I want to install a
drain. I'm guessing it to be 1/4-inch (6.3 mm?) thick steel. Tank is rated to
125 psi.

Can I drill and tap this for 1/4 or 3/8-inch pipe? Or should i get a "plug"
welded to it that I can drill & tap?

Are there rules to follow for such stuff? Is there a better n.g. to ask this
question in?

Thanks,

It is nowhere near 1/4" thick. Probably less than 1/8". I don't
recommend welding on it. But if you're going to anyway, why not just
weld on a coupling that is already threaded?