Great tip from HomeAdvisor.com

Disposals can become the source of unpleasant smells. Here’s a quick trick to eliminate unwanted odors:

To create a deodorizer, (1) Mix together a natural cleaner; vinegar, water and lemon rinds - - - (2) Freeze the mixture; Pour the mixture into an ice tray and place it in your freezer - - - (3) Place the ice cubes in your disposal. Leave the ice cubes in your disposal several times a week. The ice cubes will clean and deodorize your disposal as they melt.