Fastest way to delete all Timemachine Backups for a machine

If you're comfortable with using Terminal.app (located in Utilities folder), you can try using Unix sudo rm -r <path>/Backups.backupdb command. Note that <path> is the placeholder for the path to the hard drive where your Time Machine backup is located. Please be careful with the path that you pass to this command by ensuring there is no typo.

The complete steps are:

1. Launch Terminal.app
2. In one of Terminal.app's window, type sudo rm -R followed by a space
3. Use a Finder window to navigate to the Backups.backupdb folder, then
4. Drag that folder to the Terminal.app's window of step 2, and press the Return key.
5. You may be asked to type the password for the admin account.
6. The default prompt will reappear in the Terminal.app's window when the deletion is done.

Type man rm for documentation.

If you've got:

Operation Not Permitted

after executing

sudo rm -rf Backups.backupdb

you should follow this approach, which is adding bypass before the remove command:

sudo /System/Library/Extensions/TMSafetyNet.kext/Contents/Helpers/bypass rm -rfv Backups.backupdb

Mattorb's approach works fine.

sudo /System/Library/Extensions/TMSafetyNet.kext/Contents/Helpers/bypass rm -rfv Backups.backupdb

However the path for Backups.backupdb can be more easily entered by dragging and dropping the folder into the terminal window after the command rm -rfv[space]

It still works if you have put Backups.backupdb in trash - all that is needed is to move it to it's original disc and then apply the above terminal command from there. I hope this helps