The Drive Wiper utility within the Ccleaner program can be used either to wipe free space or the entire drive as explained here CCleaner - Wiping free disk space
I use Ccleaner all the time but have never used that particular tool. I wouldn't actually use that or any other such utility (on an actual running machine) without first making sure that I had a complete system image as well as a known good and recent backup of all my critical data.
I have used other similar utilities to completely eradicate drives prior to selling or giving away my old computers. Just to make sure there was no easy way to recover my personal data.