Q. I have a lot of fruit flies swarming in my apartment. I’ve tried a solution that I purchased in a local hardware store. Someone suggested I use apple cider vinegar to help attract the flies. Does one still have to purchase something with a “hashgacha” even though they are not using it for a direct benefit?

A. If you are using a porcelain cup or dish and you leave a non-kosher liquid in it for more than twenty four hours the utensil may become non-kosher. Being there for that length of time is considered as being cooked in that vessel, and the vessel absorbs the non-kosher liquid. (See Shulchan Aruch Y.D. 61).
However in practice, Horav Shlomo Miller’s Shlit’a opinion is that in the case of apple cider vinegar, that is likely to be kosher anyway, after the fact it may be permitted. Nonetheless, It is better to use a disposable cup.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a