Remember that stainless steel is NOT completely Rosta Frei. It’s merely stain - less. It can rust and stain, (the high temps in a fire doesn’t help), it just takes longer than plain carbon steels. And washing machine tubs are probably going to be either 303 or more likely, 304 or similar more corrosion resistant alloys.
To be even more pedantic,
Remember that stainless steel is NOT completely Rosta Frei. It’s merely stain - less. It can rust and stain, (the high temps in a fire doesn’t help), it just takes longer than plain carbon steels. And washing machine tubs are probably going to be either 303 or more likely, 304 or similar more corrosion resistant alloys.