Clearing clogs is now easier than ever and you WON'T have to open the cartridge!
Most, if not all, new Cube3 cartridges, now shipping, include a door near the hub that can be opened to access the filament while running the "Purge" function.
3D Systems has put together a great PDF document that explains how and why clogs might occur and how to clear those clogs in previous cartridge versions as well as the new cartridges with the access door.
Here is a LINK TO THE DOCUMENT.
Here are two images from the document that help you identify the two different cartridge designs.