Are there any materials besides straight metal that are kasherable for sinks? I am assuming that most people can’t afford a granite sink. As far as I recall, any sort of enameled material cannot be thoroughly kashered, correct?
At some level – and I say this only theoretically, not to rely on – one can question whether, if someone is using a drainboard, if you need to kasher a sink altogether once it is no longer ben yomo. Chazal forbade using an eino ben yomo (lest you use it when it was ben yomo), but that was a case where you are actually using it directly and intentionally. If you are using a drainboard, you are not trying to use the metal of the sink, and if anything hits it, it is an accident. Therefore, I don’t think that the gezeirah really applies (same with countertops, assuming you don’t intentionally put hot meat on it and we are only talking about accidental spills). Add to this Rav Moshe’s (Iggrot Moshe YD 1:42) point that it is hard to imagine a case where the sink directly transfers to the spoon, based on issues of iruy, nifsak hakiluach, etc.
Let’s say that all that might be true theoretically, but lema’aseh, no one uses (or should) use a sink without kashering it. But given the above, I would say that unless we are dealing with cheres (which we almost never are), we can assume that:
- the possibility that something is kasherable, enamel is basically considered to be like glass, and there is good reason to say that glass doesn’t even need to be kashered, plus
- the discussion above, plus
- that at most it is eino ben yomo, plus
- the use of soap in the past could be considered to make the taste inside the metal pagum.
This is more than enough reason to say this is not a problem. I would do an act of kashering (iruy from a kettle), and certainly allow someone to use it (same as countertops – I do not believe that anyone has to rip out their countertops when they buy a new house).