How to clean white sink that over time has stains?

Sam...Bleach usually works for me.

Hi Sam, you can bleach it, or use a cleanser like vim, that is gentle on the finish.

Fill sink with water, whereits discolored,,add a good amount of bleach and let sit for awhile. That should work, if it doesn’t add more bleach next time. For smaller areas on the bottom of sink make a paste with comet that has bleach in it, and let the paste sit awhile. Come back and scrub.

The trick is to rinse out and wipe up spills as they occur. Here are some remedies to try.

https://m.wikihow.com/Clean-and-Shine-a-Porcelain-Sink

https://www.bobvila.com/articles/how-to-clean-a-porcelain-sink/

Wipe with Coke. Honest. It works.

A baking soda and water paste, rubbed onto surface with a soft cloth should work.

All else fails use Easy Off No Fume oven cleaner in the BLUE can.

Bon Ami was recommended to me by a plumber. It cleans and whitens without scratching the surface. If it’s an older porcelain sink, bleach may yellow it like it did mine.

Try Mr Clean whitening sponges. CLR works for me if you let sit a few minutes, but don't put on spout or faucet. Dollar Tree has all these products.

Barkeepers Friend! Works great to get stains and scum out of glassware, porcelain, etc. Use with a green scrubbie.

Denture cleanser might work