I had to wipe this computer several months back. It was a pain in the keester, too.
This computer is 5.5 years old. (This is the G3 I'm talking about.) We got it in February 1998 and we've been using it ever since, and it's been accumulating junk & corruption during all that time. A few months ago, it started getting so bad that common processes were completely inhibited: The CD-ROM drive would only read commercial CD-ROM's, Software Update reset my Internet preferences, the CD burner wouldn't work, etc. So finally I stayed up half the night one night transferring data from this computer to my iMac (which had plenty of space at the time), via 100 MB Zip disks. Wow! What a pain that was, especially considering how long it took to actually read & write to & from the disks.
So I completely back up this hard drive, which is fortunately 4 GB and not impossible to back up via Zip. To actually be able to fix it, I had to boot from the Techtool 3 CD (via the burner *of course*) and use Silverlining Pro on a Zip disk to wipe the hard drive. Then I reinstalled OS 9, upgraded it to 9.2.2, and restored everything from backup, and now it's working well, with only a few glitches. Namely, drag-n-drop doesn't work with some applications (Burn, FileT&C Pro), and the CD-ROM drive still has a little trouble with non-{commercial CD-ROM's}. Sometimes.
So yeah, that's the story of this computer. Well, most of it: we have an 8.4 GB La Cie drive that flakes out from time to time, so we take it offline (and it's been offline for a while now). It's got quite a bit of stuff on it, though it's also plain HFS, which makes for 256 KB allocation blocks. I'd love to replace it, too...