The answer to 'how to clean bathtub' is to use a combination of baking soda, vinegar, and a soft cloth or sponge. Start by sprinkling baking soda all over the surface of the bathtub. Then, pour some white vinegar over the baking soda and let it sit for a few minutes to fizz and break down any built-up grime. Use a damp cloth or sponge to scrub the tub, focusing on any tough stains or soap scum. Rinse the tub thoroughly with clean water when finished.
For a more thorough cleaning, you can also use a dedicated bathtub cleaner or a mixture of equal parts water and white vinegar. Avoid using harsh chemicals or abrasive cleaners, as they can damage the tub's surface over time. It's also a good idea to clean your bathtub regularly, about once a month, to keep it looking its best.