Not only does the disposal stink, but it's a breeding ground for mold and bacteria. Every couple of weeks pour 3 tablespoons of borax down the drain and let it sit for 1 hour. Then turn on the disposal and flush it with hot water. Ice cubes help with grease build up. Put some down the drain and grind them up. The grease clings to the ice. To keep it smelling fresh, toss lemon and orange peels down the drain every other month or as needed. You can also freshen it up with salt. Dump a 1/2 cup salt, run cold water, and start the disposal. The salt dislodges stuck waste and neutralizes odor. Last, you can mix equal parts water and vinegar in a bowl, pour into ice cube trays, freeze. Then drop a couple of vinegar cubes down the disposal every week or so, followed by a cold water rinse.
I've tried them, and they work. All these helpful hints were taken from the book reader's digest extraordinary uses for ordinary things (2,317 ways to save money and time). I love this book!!!
Good luck!
Fe