What is the best way to clean tea stains from a yeti tumbler?

Not familiar with 'yeti' tumbler. Try baking soda on a damp sponge or microfiber cloth. You can soak the inside with a bit of vinegar added to water and soda.

http://www.pennyspersonaltouch.com/cleaning-blog/how-to-clean-your-yeti-or-tervis-cup

Whit baking soda and lemon juice , scrub IT whit a spunch :)

Make a paste out of baking soda add a little salt, take an old toothbrush or bottle brush, scrub inside, leave it for about 20 minutes till it dries. Rinse, it should be clean, if not, repeat, pour boiling water and put the top on, let it sit overnigh, it will still be hot. if it doesn't come out, just switch tea brands (Ha Ha)

If you use a vacuum-insulated stainless steel container or travel mug for your morning coffee, you can employ some of my favorite ingredients to clean and deodorize it.

Put a tablespoon or two of baking soda in first, then a good glug of cheap household vinegar, and watch it bubble up. Wait for the foaming action to subside, and then put the lid on (if you do this too quickly, you might encourage an explosion as the vinegar and baking soda react).

Shake the container a few times, and then pour it out and rinse with tap water. Let dry before refilling

Hi Steve, hope this helps you out.

https://www.youtube.com/watch?v=8RKoFI-PCJs

I fill my tumbler with water and Dawn and let it sit overnight. Then scrub it out with baking soda and rinse.