Ok first of all this thread is the holy grail of information. And thanks to everyone (although I'm on page 149 of the read) for helping me get my first UDS built. I found a reconditioned drum from a company and brought it home and did three burnouts on it. Sanded down the inside (although there wasn't much left in there anyway) and built a very simple UDS.
It has a 7" deep grill flat top using just the 2" bung for exhaust. I drilled three 1" holes but have found I barely need to open 1 of them more than a quarter (I use magnets - simple) of the way.
So I was fairly certain that my drum was clean but I started getting paranoid so I called the company and described the barrel and asked if it had been used to carry anything toxic or hazordous. He told me that in their reconditioning process that they burn the barrels at 1800* bearing blast them, then heat them up again are washed with a detergent and some other steps.
Basically he said there isn't anything I should have to worry about. Now he did say that if it was unlined that I shouldn't use it for storing food. So I asked him I said what about for a BBQ, he said that I am fine. I told him that I had also burned it out and sanded it down (it was painted on the inside) he said that he could have given me one that wasn't painted.
I paid $27 and could have had it without paint in it. The name of the company is Consolidated Container Company in NE Minneapolis MN if anyone is interested. They were really good people to work with and you wouldn't have believed how many drums they have.
So if you are in the twin cities area and looking for a drum this is a good place to go.
Again thanks for all the help and information you guys have given me. I made the best pulled pork I have ever made thanks to you guys and I think Levi and Strauss will be thanking you too as I'm sure that my waistline is going to be expanding real soon.