If you've finished with your USB installer and want to completely wipe the disk, you may run into trouble using default Windows method of right click>format. This is because not all of CloudReady's partitions are Windows-recognizeable, so Windows will try to format only the partitions it recognizes, leaving you with a USB key that looks significantly smaller than what you started with.
The easiest way to get your entire disk back is to use the Chrome Recovery Utility, just like you probably used to create your installer.
1) Open the Chrome App (from a Chrome system tray, or by installing then clicking "Launch" at the link above).
2) Select the small gear "Options" menu in the top-right and choose "Erase recovery media" as shown below:
3) Insert the USB stick you want to erase and BE SURE it is the right one, since the whole disk will be erased.
4) Proceed !
PS = If you only have Linux to work with, you may need an alternative method.
If necessary, use "sudo fdisk -l" to figure out the name of your device, and then "sudo dd if=/dev/zero of=/dev/sdX bs=4M" (where sdX is replaced by a,b,c etc) to write zeroes to your disk.