Mac mini end 2009 Resale : need help to install fresh OS

[Perico]

Hi everybody!
I would like to sell my end 2009 Mac Mini which has been upgraded 2 years ago with a 8Gb Ram upgrade and a data doubler kit with a 500Gb SSD from MacSales.com. So the SSD (with the OS) replace my original HD and the original HD is replacing the SuperDrive. The Mac mini is running smoothly El Capitan (10.11.6).
Here is the Data doubler kit : https://eshop.macsales.com/item/OWC/DDMM09SSD500/
and the RAM : https://eshop.macsales.com/item/owc/8566DDR3S8GP/

Now I would like to install a fresh OS to sell the Mac Mini. I plugged my USB external DVD player with the Mac OS X install DVD (10.6.2) I had when I bought the Mac Mini.
If I boot normally with my SSD with El Capitan I can't launch the Mac OS X installer (10.6.2)!
So I tried to boot with the Mac OS X install DVD (10.6.2) and of course I can install it but the software just see my HD and not my SSD. Why?
So now I have a clean Snow Leopard install on my HD and my El Capitan with all my datas on my SSD.
Of course to sell the computer I would like to have my clean install on the SSD and delete everything on the HD.
So is there a way to copy the Snow Leopard install to the SSD and delete the El Capitan install? If there is no way to do that how can I delete all my personal datas from my El Capitan install?

Sorry for the big story and my poor english. I hope you understand my issue!
Thanks!

 

[ActionableMango]

I don't know why some of those things aren't working, but I feel that you are making this harder than it has to be by trying to install a very old OS. This is what I'd do:

1. Download the ElCap installer (or use the ElCap recovery partition if it is there).
2. Install ElCap over the SSD, using the Erase option.
3. Boot to SSD recovery and wipe the HDD.

You now have a clean install of OS X on the SSD and your files are deleted from both drives.

 

[Perico]

Hi ActionableMango! thanks very much, it works!
One thing I don't undertsand, I already tried to DL the El Capitan installer in my Purchases tab but it did not work! This time it works fine! Weird!
I've launched El Capitan install, it works but did not erase my previous install so it was useless! I never seen this Erase option!
So I've formated my HD and then install El Capitan on it. Then boot on this one, format my SSD and then install El capitan on the SSD and it works. Then boot on the SSD El Capitan and wipe the HDD!
That's the complete process I've found!