Problems getting rid of large files using git-filter-branch

I'm trying to get rid of some large objects in my .git repository using git-filter-branch. These are remnants from conversion from CVS.

Q1: How can I figure out what it is in .git that takes so much space?

Q2: Where can I read more about what to do after running git-filter-branch to
removing the offending objects?

1. I ran this command to get rid of the offending files and that appears to
have worked. I can't find any traces of them anymore...

git filter-branch --tree-filter 'find . -regex ".*toolchain\..*" -exec rm -f {} \;' HEAD

2. Running "git gc" takes a few seconds. The repository is still
huge(it should be
perhaps 10-20mByte).

du -skh .git/ 187M .git/

3. I tried "git reflog expire --all" + lots of other tricks in the
link below, but no luck.

I tried the tricks I could find in this thread, but no luck:

http://article.gmane.org/gmane.comp.version-control.git/60219/match=trying+use+git+filter+branch+compress