[Pbuilder-maint] Removing a pbuilder build directory

[David Liontooth]

I'm admin on a machine that hosts a Debian developer who uses pbuilder.
Occasionally pbuilder fails, or he uses Ctrl-c to interrupt it, and
pbuilder leaves a numbered build in unstable/build/

When I try to remove the numbered build (eg 15716), I find out the /proc
and /dev directories are hard links, part of a chroot I take it. How do
I unmount/unlink these, so that I can remove the old build?

Dave