Due to the space limitations of a text message, please note that it is particularly important to read carefully, pay close attention to the context of the question, and use the answers as a springboard for further study.
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Q: We needed to kasher our sink, and left it unused for 24 hours, then afterwards, before koshering it, we drained some boiling water from a pot of pasta into the sink. Do we have to wait another 24 hours?
A: No, whatever residual non-kosher flavor that was in the sink was already deteriorated when the 24 hours elapsed.
Q: Is it important to have the yud shaped knot on my arm Tefillin be pressed up against the cube shaped body of the Tefillin by a sinew thread?
A: The Shulchan Aruch states that it is something “to be careful” about (O.C. 27:2), and Mishna Berura explains that the practice originates not only in the Zohar but also, according to the Vilna Gaon, in the Talmud itself. Mishna Berura (10) also mentions that if the sinew used for this purpose interferes with the Tefillin making full contact with the skin of the arm, it should not be used.
Q: I saw a petition signed by Rabbis against the Iran nuclear deal with both Orthodox and non-Orthodox Rabbis signed on. Are Orthodox rabbis allowed to join with other rabbis?
A: Although some authorities have adopted a stringent approach to this issue and have ruled that official collaboration with non-Orthodox rabbis in any form must be limited since it legitimizes approaches to Judaism that are incompatible with traditional Jewish beliefs, nevertheless when it comes to matters of pikuach nefesh (threat to life) it would seem that they would agree that these concerns are outweighed and set aside by the need to preserve life. (See “Thy Brother’s Blood” by David Kranzler p. 146 regarding R. Aron Kotler’s collaboration with Reform Rabbinic leader Stephen Wise for Holocaust rescue efforts (as cited by R. Reuven Mann). Rabbi Kotler was a leading opponent of official Orthodox collaboration with non-Orthodox movements.) R. Soloveitchik and his son-in-law Rabbi Aron Lichtenstein who allowed and even encouraged collaboration in non-religious matters would certainly permit it in this situation.
Q: I am renting an apartment and I don’t know what the countertops are made out of. Can I kasher them?
A: If they are made out of stone or some type of synthetic material, they can be kashered via irui (pouring boiling water on every surface). Counters technically do not need kashering at all since they don’t intentionally come into contact with hot food. It is nevertheless customary to kasher them in case hot food does touch the counters. In addition, it is seldom practical to replace counters. Due to these factors, it is OK to kasher them even if we don’t know exactly what material they are made up of.
Source: Rabbi Isaacs Blog