How do I clean a 96-gallon automated trash can?
Dilute chlorine bleach and your garden hose (assuming an adjustable nozzle that can give you a focused spray).  No scrubbing required.

You can't really prevent it from getting smelly, but keeping all the trash in plastic bags will help.  I use 13-gallon drawstring bags in the main kitchen trashcan and plastic shopping bags in my others.  Tie them off before dropping them in the trashcan.