I know it seems silly but I finally got my husband’s stainless steel travel mug gleaming like brand new on the inside !! The hubs fills it with coffee every morning and perhaps again in the afternoon at work. One would hope he at least rinses it before refilling it but who knows. If it is on the counter when I do dishes I wash it but even still it gets this build-up on the inside that drives me bananas.
The solution - boiling water and about 2 tablespoons of Borax. I let it sit for a couple of hours and gave it a few shakes. I emptied it and all these flakes came out (it was rather gross actually). I washed it and it is sparkling clean.
The hubs reaction this morning “What? Now all the flavor is gone.”
I don’t know why I bother