How do you clean tea stains off of a stainless cup?

White vinegar to cover and set in sun. At least that's how I do it.

https://www.youtube.com/watch?v=gf36bwM5SCs

https://www.youtube.com/watch?v=VuLtgBJda4U

Try pouring a 1:1 mixture of Clorox and water in and letting it sit. Rinse really well!

Get some denture cleaning tablets at the $! store. Fill cup with hot water, drop denture tablet in and leave over night. Wash and rinse well.

I always clean all kinds of cups with a good all over spray of Clorox Cleanup. Leave on for a minute or two, then rinse thoroughly. When it’s dry you can’t even smell anything. If the stain is really bad, it may take several applications.

Try cleanser with a scrubby (green ones)

Have you tried baking soda? That's what I use on my china coffee cups, but I don't know if it would work on stainless.

Baking soda is the least toxic and scrubs just as well as bleach. Chlorine gas is not good to breathe nor get it on your skin!

In Canada we us "Bar Keepers Friend" purchased at HomeHardware @ $1-5 per can, stores are outside of city in small towns of 1500. We use it for stainless steel pots & pans, on container it states for chrome, fiberglass, porcelain, ceramic cooktops, copper, brass. Learn something every day. Restaurant Supply Stores in cities, also carries Bar Keepers Friend. This will clean up your stainless steal cup, us very little moisture, and I use a green pad along with some elbow grease works wonders.