Ubuntu - Wiping hdd before selling?

[BogEyes]

What is the best way to wipe a hdd before selling, for a complete Ubuntu Novice?

Google & Forum searches still have me guessing!?

A step by step would be very much appreciated!

Thanks for any help, borgia.

 

[BogEyes]

Thank you very much for the responses!

OhEsEcks and KIA, I used both of your methods successfully.

Cheers!