Summarize this article:

Tea bags and coffee grounds can stain the enamel finish on the sink, which can be hard to remove. Throw away your tea bags and coffee grounds after you use them instead of putting them in your sink. Porcelain enamel finishes are prone to water marks and dirt buildup. The enamel can become damaged or discolored from different chemicals. For this reason, you should rinse down and dry your sink after every use. Wash your dishes, pots, and pans as soon as you are finished with them. The longer things stay in your sink, the more likely they will stain or scratch the finish.

Summary:
Don't leave tea bags or coffee grounds in the sink. Rinse and dry down your sink after every use. Remove pots and pans from the sink to prevent pot marks.