I have a SP 2010 site collection with 2000 sites and a content DB of size 400 GB. i wanted to take a back up of the site collection structure and as part of clean up i deleted all the subsites that were then in the site collection. I also cleaned up the recycle bins. The audit log tables were also trimmed. Now the size has come down to 20 GB. This 20 GB is locked up in AllDocStreams table. I do not have any contents in my site collection. The Farm is at Oct 2011 CU. How do I get rid of this junk data.

Create a new Content Database and migrate your active Site Collection(s) to it using Move-SPSite. That way it will be clean of any data that doesn't reside in what you're mo