This guide contains the basics on how to wipe a hard drive, using the multiple tools available

See also

SSD's don't need as much wiping, apparently

Internal Hard Drive

Wipe Before Windows OSD (CM's OS Deployment)

External Hard Drive (Toaster Method)

Obtain a “toaster” and the hard drive to be wiped. Setup the toaster and hard drive

Wipe Using Windows File Explorer

Wipe Using Windows Disk Management

Windows 7

Windows 10

Either Internal or External HDD

Using the Multiboot USB tool

Alternative to the Ultimate Boot CD method

Using Windows Installer with USB boot

This method uses a USB that is used to install Windows. However, we just want the wiping/formatting capability this method provides, i.e.: AVOID INSTALLING ANYTHING.