How should I best go about installing BleachBit under OpenBSD?
An older version (0.6.4?) was ported to NetBSD and many or all of the changes were taken upstream, but the NetBSD porter didn't seem to continue it. As stated, BleachBit is written in Python and PyGTK. There may be minimal changes to the Python code, and maybe some in the CleanerML (mostly XML) which defines which files should be cleaned.
If you have any issues, best to ask in an OpenBSD forum or on the BleachBit forum.
(I am the BleachBit author.)
There is currently, as far as I can tell, no port of BleachBit specifically geared towards BSD, never mind OpenBSD. It appears to be written in Python, however, so you may have luck downloading and running the sources from here.