Garbage disposals are one of the best kitchen accessories ever invented.
However, if you do not flush water through the disposal after using it, food particles will be left behind. Over time, bacteria will develop creating a foul odor.
To remove the odor, it is necessary to actually remove the sludge from the sides of the disposal.
You can attempt this yourself or you can have a plumber come and service the disposal for you.
To prevent the disposal from accumulating sludge, thoroughly rinse out the garbage disposal after every use.
The best way to do this is to fill the sink with warm water and a little dish washing liquid. When the sink is nearly full, remove the stopper and turn on the garbage disposal. This creates a whirlwind action and will effectively wash the disposal. However, it will only work to clean the disposal after use.
If you have hardened debris that is causing the foul odor, only a plumber can remove this and solve the problem.