I'm currently running an iMac Retina 5k, 27 inch, late 2015 desktop with 4 external HDD's. I had previously installed OSX High Sierra BETA 10.13 ( with periodic updates ) to the Macintosh internal HDD. When Apple announced the release of the Public version, I wanted to install that version but was put off because it was said the public version would not support the fusion drive on my system , and in effect would not allow installation on my system using the Macintosh internal HDD/Fusion Drive. I decided to use a 3TB external drive I had installed previously, and successfully loaded the new OS and am running successfully from the external drive at present. Wanting now to erase the old OSX Beta from the internal Macintosh drive, I have tried using Disc Utility without success. When I try, the "erase" function seems to start but nothing happens ( I've waited over an hour to see if it was just slow ) I have browsed through similar threads and tried several "Terminal" commands again seemingly without success. I have also noted that after running the Diskutil CS List command, whatever I've managed to do, has somehow erased "Core Storage". ( ? ) Any suggestions would be appreciated - as said, I simply want to erase the Macintosh internal drive so it can be used. Attached is a screenshot of the DiskUtil list commands.