Deleting all user data from Time Machine after backing to disk? I have backed up everything to my Time Machine backup disk. How do I securely delete all data that was backed up from my MacBook, including past Time machine snapshots?

I have only recently started using Time Machine and am not sure if deleting my data completely would also delete past snapshots?
You can erase your external disk using Disk Utility. Select your disk and choose Erase. If the disk is not solid state and you want to securely erase the data, then select Security Options and choose a level of erasure.

To delete all local snapshots, you can use tmutil's ‘deletelocalsnapshots’ verb.

tmutil listlocalsnapshotdates | tail -n +2 |
  xargs -0 -n1 sudo tmutil deletelocalsnapshots