It depends on the software, how many times you write over the items your deleting.If you really want to do your whole HD, I believe you'll have to un-delete your whole HD, then write over it with that program if it offer's both.
When you delete somthing your not really deleting it, your just putting it in another place on your HD. When you want to "wash" those items that were deleted your not really getting rid them, your just writing over them and rendering them useless and unrecognisable.The more times you write over an item, the more it's not recoverable.