My camp cup, which is blue porcelain over tin, has never seen soap, though none of my tins have generally, the cup. certainly.
And it's right to call it seasoned. More along the lines of the same thing as cast iron ware, rather than adding taste. It is rather that it does not have the taste of the soap... albeit that it does 'normalize' like cast iron does.
THe same goes with my EDC go-cup and the favored morning cup, which has been my father's before me for many years - a White Castle cup.... only washed when a woman was around...
And my current one, 'Best Farter (Father)' cup, given to me by my daughter, which makes fart sounds every time you pick it up, and makes me giggle even yet, so much that keeping the coffee where it belongs is a problem... But due to its electronics, it has an excuse to avoid the sink.