Hi all
Not done it myself yet but as far as the gas bottle goes most people fill it with water, as mentioned above, and leave it for a few days just to make sure there's no gas pockets anywhere.
As far as the drum, mine held motor oil, I just made sure the holes on the top were not plugged by anything and then ran a grinder with a flap disk around the inside edge so no sparks went inside the drum anyway.
I uploaded a write up on how I did it here:
https://www.dropbox.com/s/7lndnbdgkom2h ... w%20To.pdfI hope it may be of use to someone