Software Update Server (SUS) - default server address

I was wondering what the "Default" address to Apple's SUS.
I have used the app "Set Software Update Server" to set the computers to our local SUS, but I am having issues returning them to apples SUS.

I have done the following:

*To undo the change and point all users back to the Apple Software Update server:*

*defaults delete /Library/Preferences/com.apple.SoftwareUpdate CatalogURL*
*Note: Replace "[URL]" with the URL of the Software Update server, including the port number and the name of catalog file (index.sucatalog). For example, http://su.domain_name.com:8088/index.sucatalog*

Any other suggestions would be welcomed, I have also deleted the same prefs on all accounts, and restarted the machines.