The answer to 'how to clean bathtub' is to use a combination of baking soda, vinegar, and a soft-bristle scrub brush. First, sprinkle baking soda all over the tub and let it sit for a few minutes to help break down any soap scum or grime. Then, spray or pour vinegar over the baking soda and let it fizz for a minute. Use the scrub brush to gently scrub the tub, paying extra attention to any tough stains or buildup. Rinse the tub thoroughly with clean water when finished.
It's recommended to clean the bathtub at least once a month to keep it looking its best. If you notice any cracks, chips, or other damage to the tub, it's best to call a professional plumber to assess the issue and determine if repairs or replacement are needed.