According to Frank Black, the PIxies are staying away from alcohol to support Kim Deal, who has had problems with drugs and alchohol. Take it away, contactmusic.com:
"'Kim said to me, 'Charles, I really hope you understand that I really want this tour to be a dry tour because I'm not drinking right now and I don't want to start drinking again.' Once I realised that, I was like - oh this is going to be a lot easier. "The fact that she's not drinking has caused everyone else not to drink, because we're all trying to be supportive, and as a result everyone is pulling together. "No one's drunk, no one's high, everyone's on top of it and not tired because they're hungover."
Using hard drugs is very Overt, but so is being what we used to call straight edge. In other words, making a statement either by using or not using drugs/alcohol is Overt.