If someone cans using Ball brand glass canning jars (and new lids are used every time, so nothing to worry about with those), In the normal canning process, the jars are boiled to sterilize them prior to the addition of food. Is this sufficient to kasher the jars so that we do not have to worry if the jar previously contained dairy or meat?
Whatever one puts in the jars is effectively cooked in the jars as one has to bring it to a high heat for a sustained period of time.