Tip on How to Monitor Disk Utility Erase Free Space
When you use the Disk Utility Erase Free Space option, it can sometimes appear to hang and the progress bar isn't always a help.
By accident, I discovered that if you run the Activity Monitor and select Disk Usage, you can in fact monitor progress. The Space Free will gradually tick down, sometimes as slowly as 100K/sec, then when it hits zero, it will quicklt tick back up. If you observe this, just let Disk Utility complete to avoid any issues; Activity Monitor makes it easier to be patiet about this.
Hope this helps.