I would use a 50/50 mixture of hydrogen peroxide (3% solution commonly found at pharmacies or grocers) and water. Fill the tube and wait a few minutes (5 minutes should do). The same mixture (or straight hydrogen peroxide) is often used as a mouthwash and disinfectant. Then rinse with water. It will leave no soapy or other noxious taste or odor. But I’m sure there are lots of alternatives.