I can't find brush cleanup. I selected the brush, however, and selected menus Brush -> Make Structural. I recompiled, or tried to, and it still shows a leak through a solid wall... wait, I got it. Turns out, through resising and whatnot, I managed to make the wall 1 unit thick, with one side caulked. It figured it was "caulk" and therefore invisible. I resised the wall, causing a slew of emberassing leaks, but at least I got it. I think. I'll report back if the problem comes up again.
EDIT - It's back. I am including a link to the next screenshot. It features the XY view. Someone explain this, please!
Click on it a couple of times to enlarge the pic to full size.