If you are struggling with stubborn sink stains, you will find products that you already have in your kitchen can help you remove the stains.
USED BLACK TEA BAGS - Place wet used black tea (orange pekoe) bags on the stain. Tea can remove many stains, especially from white porcelain.
WHITE VINEGAR - Vinegar is also an excellent cleaning agent. Clean your sink regularly with vinegar. It is almost as strong as bleach, yet gentle enough for you to consume it if you wanted to.
POWDERED CLEANER - For a very stubborn stain, wet the spot with water. Sprinkle a powdered cleaner such as Comet to the stain. Let it set for 30 minutes and then rinse it away.
BLEACH - If you still have not removed that stubborn stain, you can use household bleach. Pour the bleach directly on the stain undiluted, then rinse the area thoroughly. I usually use bleach only as a last resort.