Drop ice cubes down the drain and disposal, using tongs or an ice pick, until the disposal is filled with ice. Add 1 cup of rock salt down the drain.
Turn on the disposal and let it run for about five seconds; this is longer than you may think compared to how long you usually run the disposal. Let the disposal chop all this up, which subsequently clears the sludge.
Run the disposal at least one minute later to see whether it runs properly.
Cut a lemon into slices and place the slices within the disposal to remove any odor that remains from the sludge buildup.
Run warm water down the drain with the lemon pieces in the disposal and turn on the disposal to chop up the lemon and freshen the drain/disposal.