How do you remove the dark rings around the taps?

Lemon. This citrus fruit also has disinfectant and bleaching properties, which help remove stains. Rub half a lemon directly onto the dark stain, let it sit for a few minutes, and then wipe it off with a cloth. Repeat this if the stain persists.
Borax. This is one of the most powerful agents for removing stains from virtually any bathroom surface. Apply borax directly to the stain and then pour vinegar over it. After 20 minutes, scrub with a sponge, rinse with water, and dry thoroughly. Wear gloves and a face mask while applying borax.