To clean an acrylic bathtub, soak the inner tub surface in warm water mixed with dish liquid, wipe off the stains, rinse the inner surface, rub the stains on the rim and outer surface with baking soda and dish liquid respectively, and rinse it. Then, dry and polish the tub.
Clear the bathtub of any items, including soap dishes and tub mats, and wash them outside the tub. Fill the tub with warm water, measure four squirts of dish liquid, and add them to the water. Mix to form a uniform solution, and let the tub soak for 30 minutes before draining it. Using a sponge, wipe the tub's inside surface to remove any loosened stains. Sprinkle baking soda on a sponge, and rub the sponge over any stubborn stains until they disappear before rinsing.
To clean the outside of the tub, sprinkle baking soda on a sponge, and start by rubbing the sponge over the rims of the tub to eliminate any stains. Rinse the rim. Next, apply dish liquid to a wet sponge, and use the sponge to wipe the whole outer surface of the tub. Scrub any dirt off the fixtures, wall and corners with a toothbrush, loosening any soap scum with an all-purpose cleaner. If necessary, continue scrubbing to break down any stubborn scum.
Once clean, rinse the surface, and blot it dry with a clean cloth. Finally, apply car polish to the tub surface to restore its shine. The polish also facilitates future cleaning.