Soap scum in tubs and showers
Since preventing soap scum build-up is a lot easier than cleaning it, squeegee water off shower walls and doors after every use or wipe them down with a towel. For tile walls or frosted shower doors, apply a light coating of lemon oil periodically to help prevent build-up. For a porcelain tub, apply a light coat of boat car wax to the sides (never the bottom) of the tub.
If it's too late for prevention, use decreasing agent and lots of elbow grease. Get a good alkaline soap scum remover at a janitorial supply store or dissolve a handful of automatic dishwasher detergent in a bucket of warm water. Cover the affected area completely and let your cleaning solution soak for at least 15 minutes. Do it right after a shower when the walls will be wet. After soaking, use a stuff scrub brush or a white, nylon-backed scrub sponge to clean the walls. You may need to soak and scrub a couple of times to get rid of all the build-up. Then rinse well with clear water.