Directions For Use Apply to Dry & Clean Glass! Your suction cups work best when placed onto clean and dry glass. They'll turn white and lose ability to maintain suction after a period of time of use in water. You can wash them with dish soap or vinegar and rinse them thoroughly with warm water. Replace Your Suction Cups! The suction cups do wear out over time. Do not expect a suction cup to last forever. Most importantly, you need to replace the old and worn suction cups timely if they still can't stick properly to dry and clean glass.