Yeah, since I am no chemist, I'm always afraid to use anything but vinegar - but you should use the 25% highly concentrated variety for getting rid of build up, I often mix it with 2/3rds 50/50 water and when boiling, it clears even old iron pans out. With wine vinegar, I never really got what I wanted results wise, i think that's usually ~7%ish. I also use it at it's 25% ratio, undiluted - But if you even dilute the wine vinegar, it's not doing much at all in my experience. I do use soda (sodium carbonate) for getting rid of tea residues in stainless thermos with great, actually astounding results also when cleaning glassware for marmalade and such things. But I think it erodes aluminum and other metals. Citric acid I never really used much, tbh - it works too, tho. It stitting on my shelves. But afaik it's not as aggressive towards aluminum and other parts, since, unlike soda and water, it's not an "alkalische lösung" (not sure what high schools in the u.s. call that, google is fren.) I would try with stronger vinegar first.