Since upgrading, the Secure Empty Trash option is missing, although the online help has not kept up and suggests that it is still there!
There is no option in Finder > Preferences to switch it back on (as the help suggests).
Does it still exist? - I had it as the default to properly empty the trash with no residual ability to recreate the files trashed.
MacBook Pro with Retina display, OS X El Capitan (10.11)
It appears Apple has changed the way the trash is emptied.
Right or control click the Trash icon then right or control click file then click: Delete Immediately
That removes the location and overwrites the file so it can’t be recovered ever by anyone.
From here > http://www.macobserver.com/tmo/article/el-capitan-beta-the-delete-immediately-fe ature
It was removed because it wasn't doing what it was supposed to do and was unnecessary on SSD's.
Search the Security bulletin for "Secure Erase"
About the security content of OS X El Capitan v10.11 - Apple Support
Unable to use Secure Empty Trash
