Yeah that's a weird design, usually it's just a plug at the bottom. I guess it's supposed to be used with something like this:
Radium Oil Catch Can Drain Kit (1) - RAD-20-0024 van Radium Engineering - Monkeywrench Racing -
If you can find a small petcock, you fabricate this kind of drain hose. Otherwise, just replace the bottom bit with a plug, but since it seems you can't open the can, be prepared to have oil everywhere once you drain it...
I've got this one:
Splitflow Blow-Bye Oil Catch Can
It has a plug at the bottom but the bottom hole was too small for the plug, once you screw it in, there's no way you can remove it. Anyway, since you can just unscrew the can and take the bottom part off, it's very easy to drain.
It's baffled (well, kinda) and filtered but I've added steel wool + an additional hose inside to force the vapors down and maximize the condensation.