Step 1: Safety, Disclaimer, and Tools
Cat crap is nothing to sneeze at. It can carry many diseases and make you sick. Wear gloves and wash your hands afterwards. If you're going to scrub vigorously you might want to wear a face shield. Although not absolutely required, I highly recommend shutting off the water line and disconnecting the power.
If you screw something up, I am not responsible. You assume all responsibility for your actions. Your mileage may vary. Look both ways before crossing the street. Don't drink and drive. Eat your veggies and above all, be good humans.
You need a drill (don't worry, you won't be damaging your CatGenie or voiding any warranties), a pitcher (for water), and maybe a towel. That's it.
Step 2: Get At The Impeller
To use the drill you have to get to the impeller, which involves removing the "hand" (the scoop) hood and the motor assembly. No tools are required for this - just lift them off.