PrivaZer will clean up anything that CCleaner misses. But for general maintenance, CCleaner is the best IMO. And yes, PrivaZer is safe. The scan can be long depending on the state of your computer, and I recommend running it when you're not playing games or something.
CCleaner has it too, go to Tools>Drive Wiper select how many pass you want... But still prefer Privazer its safe, just reminder if you choose privazer remember to tick "Save registry".
This depends on what your meaning,
Are you wiping the drive for a reinstall, or wiping it to sell ?
Or are you just cleaning it up ?
wiping it completely is hard on the HD especially if you up the number of passes.
Ccleaner and Privazer are very powerful tools so be careful and read up on what ever it is your trying to accomplish before you attempt to wipe a drive.
I have used Ccleaner Pro since it's conception and love it.
PeAcE
I use the Tools System Clean-up orDriveCleanser from Acronis True Image 2016 with 8 methods available (for exemple, the Gutmann method : see Secure Deletion of Data from Magnetic and Solid-State Memory).
When I was young, I have used BCWipe (I loved the option : Wipe File Slack space to clear previously deleted data)