Wiping free space on HD

Has anyone here ever used CCleaner to wipe the free space on a HD. Now with a question like this everything is relative and I am just looking for a general idea. 1TB harddrive in use for a year. Yes a lot to overwipe. I guess the question is did CCleaner work for you and did say 3 wipes take forever. As in days or even weeks? Were you able to use the computer while this evolution was taking place without noticing any difference? Or, did you use a different free program for this job.
Any help would be appreciated. theoldghost

yes, yes, yes, yes (8 cores)