The singer checked in to the rehabilitation clinic in 2005 in a bid to kick his alcohol addiction, but found the experience akin to spending time in a "concentration camp".
He told Details magazine: "I hated it. It was like a concentration camp - well, I can't say that, I've never been in a concentration camp. But for me, it was.
"There's a lot of dogma that goes with it, and there's the whole AA (Alcoholics Anonymous) thing, and for a lot of people that works. I didn't necessarily follow that."
Though the stint helped him conquer his alcohol dependency, Joel admitted that he still drinks occasionally.
He said: "It was good. I dried out. And it was probably one of the best things I ever did, because I realised I was just drinking too much, and I really don't need to do that.
"Once in a blue moon, I'll have a glass of wine. But I'm very afraid of going beyond that. I don't want to be out of control."
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