Trying to DBAN 2009 Mac Mini
If you have a hard disk drive (HDD), the use of a third party tool is unnecessary. You can boot to macOS Recovery over the internet and use the Disk Utility application to accomplish this task.

The possible security options available are as follows:


US Department of Defense (DOD) 5220-22 M standard for securely erasing magnetic media. It erases the information used to access your files and writes over the data 7 times.
DOE-compliant 3-pass secure erase. It writes two passes fo random data followed by a single pass of known data over the entire disk. It erases the information used to access your files and writes over the data 3 times.
Write a pass of random data and then a single pass of zeros over the entire disk. It erases the information used to access your files and writes over the data 2 times.


Note: The security options available can very from type of download chosen and the model/year of your Mac.

USB Flash Drive Method.

See the website How to create a bootable installer for macOS for instructions.

You will need to download OS X El Capitan from the Apple website: How to download OS X El Capitan. The upgrade can be used with your Snow Leopard OS X 10.6. Although, you might need to make sure you have first upgraded to OS X 10.6.8. If this case, try downloading the Mac OS X 10.6.8 Update Combo v1.1.

Boot from the USB Flash drive and use the Disk Utility application.