Put the shine back in your porcelain sinks and bathtubs by giving them a good scrubbing with full-strength white vinegar, followed by a rinse of clean cold water. To remove hard-water stains from your tub, pour in 3 cups white vinegar under running hot tap water.
Enameled steel bath tub?
If you’ve soap scum or water deposits,
I would use a soft scrub or bar keepers friend type of cleaner and use a circular polishing motion.
After rinsing well, hand dry with a towel in a circular polishing motion.
After cleaning it well, use an auto carnuba wax product and buff it well. Be sure to have a bath mat or strips to give you some safety traction.