Getting rid of mold and mildew on caulking in the shower, sink, and other areas of the bathroom can be next to impossible no matter how harsh a chemical cleaner you use. But here's a trick that works for cleaning this up. Soak cotton balls in bleach and place them all along the caulking that has the mold or mildew problem. Push them into the caulking so that they make contact. Leave them there over night. In the morning, you can remove the cotton balls and your caulking should be nice and clean.