The thongs I use for sport with leggings and work are a mix of polyester and spandex. I want them to last as long as possible.

I experimented a bit with one: I made a baking soda paste, applied it to the stained parts, let it sit for an hour, hand scrubbed it, rinsed in cold water, pressed the thong to get rid of as much water as possible, let it to air dry. Am I being too careful?

Baking soda removed all stains.

Do you only hand wash your undies?