How to clean a garbage disposal:
1) buy a toilet bowl cleaning brush
2) Use a permanent marker and write "disposal Brush" on the handle.
3) Put some light liquid soap (or other cleaner) onto brush
4) Push brush into disposal and turn clock-wise and counter clock-wise
5) Run the water and SLOWLY pull brush out all the while turning the brush. I usually put my hand near the brush so it doesn't splash gunk all over the place.
6) Rinse the brush under the running water
7) Put the brush under the sink so it doesn't get mixed with the real toilet brush
8) Run the disposal as normal (no brush in disposal - see, it's under the sink already!)