Willam gave an interview to EW and was still coy about what the actual rulebreaking was:
'RuPaul's Drag Race': Disqualified contestant speaks out | PopWatch | EW.com
Sounds like they are teasing it until the Reunion episode at the end of the season. But they threw a bunch of hints by showing Willam throw up, and his looking quiet and shaky in the workroom, and that close-up on his hand shaking in the Illusions Lounge during Untucked -- my guess is that he went AWOL and partied somewhere without the show's knowledge, or maybe was stashing alcohol/drugs in his room (if that's against the rules, who knows with this show)...
But they are definitely trying to save the details for the reunion. That was the most staged/manipulated Untucked I've ever seen. Obviously they were told they couldn't talk specifics on camera, because everyone chose their words very carefully, and it was edited weird, where nobody talked about Willam at first, and then suddenly in the second half, everyone knew he broke rules and was talking about it (yet it was still before the lip-synch). I didn't appreciate the blatant fakery this week, this show hasn't had that kind of reputation before now.