Although white bathtubs offer a clean, inviting look in any bathroom, grime can easily make a white tub hard to handle. Hard water stains, dirt and mildew in your tub quickly can make an otherwise clean bathroom look dirty and uninviting. However, removing any hints of dirt from your bathtub once a week will help you to stay on top of the tub's appearance and bring a neat, shiny look back to your tub.
Put on rubber gloves. Make sure the bathroom in which you are working is well ventilated by opening the windows and door.
Spray the walls of your white bathtub with a commercial all-purpose or bathroom cleaner. Apply warm water to the areas you sprayed, and follow the manufacturer's instructions for scrubbing the tub. When using a sponge or cloth, scrub from the top of the tub walls down to the tub floor, which will give the floor the full benefit of a soaking to dissolve the build-up.
Purchase a trisodium phosphate substitute, and mix 1 tbsp of it with a gallon of hot water if you have heavy dirt deposits, soap scum and grease in your white tub. Pour this mix into the tub, and scrub the dirty areas. Also, if you are trying to get rid of a stubborn stain or ring, particularly in a white porcelain tub, apply an oven cleaner to the stain, following the manufacturer's directions. Let the cleaner sit for a few hours before rinsing it off.
Apply hydrogen peroxide or chlorine bleach to other particularly tough stains in your tub. Rinse off the bleach after a few seconds of use. Be aware that bleach will not work on removing rust stains. Additionally, you can mix a solution of salt and turpentine in equal parts, and use this and a sponge or cloth to rub away yellow spots on your tub if you have an enamel tub. Rinse the tub thoroughly afterward.
Apply a natural cleaner to your white tub to further get rid of hard-to-remove stains. For example, mix warm water with baking soda to create a pasty solution you can apply to your tub before scrubbing to help remove soap scum and dirt. You also can pour 3 cups of white vinegar into your tub under hot running water if you have a porcelain tub, and allow the water-vinegar mix to sit in your tub for four hours. Allow the water to drain, scrub any stains off and rinse the tub with cold water.
If you use an abrasive scouring powder as your bathtub cleaner, make sure the powder is fine. Many powders contain sharp, hard particles that will scratch the surface of your white bathtub -- particularly if your tub is made out of porcelain. The scratches will become homes for soap residue, dirt, hard water deposits and grease.