Thermos Needs Cleaning

I know this thread is old but I came across it while looking for info on cleaning my thermos of coffee junk. That thing was black, black, black on the inside. But now that I want to use it for tea the black had to go!
Anyway I had denture cleaning tablets but even the tablets only lightened the black in two tries (overnight soaks). So I read here about using Oxyclean and Smartsoak, but given my location in Mexico, those things arent possible just now. However, I saw that both Oxyclean and Smartsoak are primarily sodium percarbonate. After a little more research I discovered that sodium percarbonate breaks down into sodium carbonate and peroxide in water. Ah! I have baking soda ( Sodium bicarbonate) and peroxide! So I put about 2 tablespoons each into my stainless steel travel cup and filled the rest with boiling water. Instantly black gunk started foaming to the top. I soaked my cup for no more than 5 minutes before I got excited and decided to pour out the mix and check progress. WOW! My cup was as clean as new! No joke! Like new! Years worth of nasty, black, coffee grunge gone in 5 minutes!
Please try it for yourself. I am so excited by this discovery that I have to share it.

I was actually just trying to clean the tea stains from my stainless steel thermo earlier today! I’ve realized that the magic erasers do a really good job picking up the stains!

Vinegar will solve your problem.

And one thing that’s worked with stains on glass is wetting the vessel and adding a bit of salt. Leave it for a few min. Then scrub off the stains with a sponge. But I’m not sure how well that’d work with the inside of a thermos.

Instead of starting a new topic, I decided to resurrect this old discussion topic for a new generation of steepers trying to keep things sparkling! I have been wholly impressed by the power of cleansers containing oxalic acid to remove tea stains from stainless steel vessels, plastic bottles, glass cups, stone and composite sinks, porcelain, china, stoneware and other ceramics. I use a wet cloth or sponge scrubber with either Zud or Barkeepers Friend and a very light wiping pressure, with sometimes a soaking. Usually the stains are gone within seconds. It takes virtually no pressure or scrubbing, so scratching is not a problem. Then I just rinse well or run through the dishwasher to eliminate residual oxalic acid (fear of ingestion leading to kidney stones). I see @ashmanra and @Fergy also mentioned Barkeepers Friend some time ago. I am not familiar with OxyClean, but it may also contain oxalic acid. I am intrigued by those mentioning citric acid and I’ll give that a try soon, as I have it on-hand for canning. I, too, found vinegar to be weakly useful, though it is good for lifting mineral scale from my kettle!

OxiClean’s active ingredient is sodium percarbonate which breaks down into hydrogen peroxide and sodium carbonate. It is supposed to be a very environmentally friendly cleaning option and I love that I walk away and come back twenty minutes later to a clean teapot or infuser or stained cup, whatever was getting the special treatment that day.