This film can be a result of many factors, some internal to the home, such as a water softener or plumbing materials. It may also be related to the condition of the water coming into the home. Minerals in water can leave deposits, which can be left behind on toilets and dishwashers as the water evaporates. Rings on baths and showers can be scum left behind as the water evaporates or soap or shampoos reacting with minerals in water. Black slime is usually mold/mildew that thrives in moist areas like bathroom toilets and tiles where it is wet and warm. The film that develops on sink stoppers is bacteria and residue build up. Usually, the customer will need to clean the area with a commercial cleaner that contains a disinfecting agent, such as chlorine bleach.