The built-in Disk Utility does everything you want.
To wipe a drive:
Open Disk Utility (It's in ~/Applications/Utilities)
Find the drive you want to be wiped in the sidebar, and select the root drive (not the partition):
Go to the erase tab:
(optional) If you're paranoid about your data, there's a button Security Options. Clicking it brings up a dialog ...
For paranoid shredding, install GNU coreutils and use its shred program.
Disclaimer: any solid-state drives, USB sticks, and memory cards that use wear levelling can't be guaranteed to be fully shredded. This applies to pretty much any disk-wiping software unless they can get beyond the wear-levelling layer.
You've not mentioned what you've tried so far, so I'll suggest two that I've been made aware of in forensics classes. Its useful not note that while these arn't completely foolproof, they do implement the one proper way to clear slack space in windows - using the defragmentation API to overwrite the slack space. If its a file you absolutely do not want found,...
I recommend Eraser. To quote:
Eraser is an advanced security tool for Windows which allows you to
completely remove sensitive data from your hard drive by overwriting
it several times with carefully selected patterns. Eraser is currently
supported under Windows XP (with Service Pack 3), Windows Server 2003
(with Service Pack 2), Windows Vista, ...
anyway... in general i would advise to use DBAN (or it's unofficial fork dban) to wipe complete disks:
it would be the universal method because it works from it's own bootable iso, is therefor platform independent, also free (as in speech and beer),... you only need to create a bootable media (CD, DVD, USB, etc.) and start from it.
an interesting option ...
You can't find such portable tool.
More precisely, it can be portable as "no installation required" but it can't be portable as "no administrator privileges required". Direct disk access requires administrator on Windows.
The only way to erase free space without administrator privileges is create a new file taking all empty space on the partiotion and fill ...
Darik's Boot and Nuke (DBAN for short) is probably what you are looking for (as long as you're not trying to wipe an SSD or individual disks in a RAID volume). It's free; the download is a bootable .iso that you write to media yourself. All you do is boot, select one or more disks to wipe, and tell it to start. It's then completely automated.
The web site ...
if you want a really free and not only gratis tool you should use BleachBit:
it is free software (GPLv3)
multi-platform: Linux & Windows
easy GUI: just check what you want to do
shred files/folders to prevent data recovery
overwrite free disk space to hide previously deleted files
and much more advanced features...
additional features for windows:
When my company was looking into this we tried out a number of solutions such as the ones you listed and the main issue was SSD erasure. Most of them say they erase SSDs but all they do is enable Secure Erase and say that it was erased. That's all fine and dandy except there are tests that show Secure Erase does not work 100% of the time for SSDs.(see Grupp ...
You can use WipeFreeSpace which runs on linux. Supports various filesystems including FAT32 (Win98).
You have to pass trough manual building process, as there is no binary...
Or you can use hacers tool THC-SecureDelete.
For firs try I do recommend you to backup all the data first, so therefore tar the data to another disk and wipe whole disk and tar it ...
You drive is small and failing, so I doubt that you will be reusing it.
I would suggest a "hardware wipe", which is always quicker than software.
a Black & Decker drill
a drop from a tall building
bury it in the garden
use your imagination for more. None of those should take 18 hours (unless you dig a really deep hole in ...