Sounds like your drain line is clogged with crud and needs to be taken apart and physicaly cleaned out. This tends to happen if you dump things like potato peels and such into the disposer, it turns to a slimey gooey muddy mess after time and clogs it up. Draino or Liquid Plumber isn't going to save you at this point, you just have to take the drain line apart and clean it out all the way through the S trap. | 
Disposal Fills with water 
