In article .net,
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,

You could try avoiding modifying the tank altogether. Get a pipe
cross, mount the tank above so the pipe has to go up to get into the
tank, then have a six to eight inch (assuming it's 3/4 or 1"--longer for
thinner pipes unless you don't mind draining more often) leg of pipe go
out the bottom of the cross to collect water and gunk. Stick a drain at
the bottom of that pipe. Then use the remaining two sides of the cross
for inlet and outlet.
Not pretty or very mobile, but works OK.

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