I found wikipedia actually gives a good description of magic mouthwash if you want to start there . I'd suggest getting a good recipe from a trusted source. Maybe call up Sloan and see if they have anything they can suggest.

When I had my biopsy done back in 2008 my "thing" also got "smaller". This was because after they biopsied a piece off, it was no longer rubbing against my teeth, getting iritated, and swelling. It is possible that it might be shrinking, but I'm sure Sloan will be able to tell lots of info from it and the reports no matter the size.

Good luck!