How to remove such stain in kitchen sink?

[Kayelle]

Had a enamel sink years ago and i use the hot water and Clorox bleach, I whiten it right it every time and no damage. Then remodeled kitchen and all stainless went in.

Glad to hear you've used the same method I have letscook.
Regular liquid laundry bleach and water is the best bet for the old sink. If it's safe for your clothes, why wouldn't it be safe for an old sink?