Brush Cleanup is located at the top, with the other menus entitled "File" "Edit" etc... look for Plugins -> BobToolz -> Brush Cleanup
Also, there is a blue and green arrow circular icon with a bunch of other icons on toolbar, which is Brush Cleanup (simular to a recycle symbole, but blue and green...)
Normally, if brush cleanup doesn't work, I delete the bad brush and remake it, which usually solves the problem (unless I have a stupid error... like... a patch going through a wall)
Also, a tip: Go to Edit -> Preferences -> BSP Monitoring and turn off "Stop Compilation on leak"
That way if there is a leak the compile will continue. It will still notify you of the leak, and show you where it is.
OK, I figured out what the problem was. Somehow, I managed to accidentally use caulk_acid on the outside of the brush instead of regular caulk.
Don't feel bad, one time I was working a on a cool map, after a few days of work I compiled and loaded... but fell through the floor (wasn't worried about the leak)
After much thought, recompiling, and examing my map over and over again, I soon realised I made everything in caulk_nonsolid... lol.