Fill the sink or bucket with lukewarm water and a few tablespoons of dish soap. Boiling water can be dangerous to the user, and it may melt the mouthpiece.
Put the mouthpiece in the water, and allow it to soak for 20 minutes.
Remove the mouthpiece from the water. Use the mouthpiece brush to clean inside the mouthpiece, then clean up any residue on the outside of the mouthpiece. If trouble spots exist, repeat cleaning steps.
Run the mouthpiece under running water to clean out any remaining residue. Dry the mouthpiece with a towel or lint-free cloth.