Secure Wipe a Disk Before Surplusing

via Graphical User Interface

Insert bootable external drive
Restart computer and hold down 'Option' key to open up Recovery Mode
Select the inserted bootable external drive
Select 'Disk Utility' from the macOS Utilities page
Select the desired internal drive and select Erase
Select 'Security Options' and drag the slider to the third option or 'Most Secure' to ensure that the drive is completely secured.
Click Confirm and begin the wiping process. (Note: This process may take hours to complete.)

Insert bootable external drive
Restart computer and hold down 'Option' key to open up Recovery Mode
Select the inserted bootable external drive
Select Terminal from the 'Utilities' tab within macOS Utilities
To see a list of disks, issue the following command within Terminal:
```
diskutil list
```
Use this list to determine the desired drive to wipe.
Issue the following commands within terminal:
```
sudo diskutil zeroDisk /dev/disk4
sudo diskutil randomDisk /dev/disk3
```
Use zeroDisk if zeroing out the disk for reuse. Use randomDisk if sending it out for surplusing
Make sure to issue the correct disk when wiping! Any errors will result in lost data!