Trash can odor is a common problem for just about anyone who has a garbage can. Fortunately, it's fairly easy to remove nasty smells that accumulate.
Baking soda has long been used inside refrigerators because of its ability to absorb odors, and you can use it in your can, too. Sprinkle it on the bottom and let it work its magic. You can add more if the smell is really bad. One great thing about this method is that the baking soda will also help you clean the inside of the can.
Bleach is great at cleaning and killing whatever causes smells. Add 1/4 bleach to 2 gallons of warm water, make sure it comes in contact with all sides, then let it sit for a while before washing it out. Make sure you do this in a well ventilated area, and NEVER mix bleach with ammonia or any product that contains ammonia since doing so will create a deadly gas.