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Using hot water in a sink on Pesach:
One is initially to be careful not to use hot water that is over Yad Soledes [110° F] on Pesach, in a sink that is not Kasherable. This applies even if one has a sink insert. Thus, one should not turn on the hot water to the point of Yad Soledes and is likewise not to pour hot water into the sink so long as it is Yad Soledes, even if it is in a Keli Shelishi or Revi’i. [Accordingly, if one has a pot with hot water, he is to wait until it cools down prior to pouring it into a non-Kashered sink. One can mix cold water into the hot water in order to achieve this quicker.] If the water is warm, below Yad Soledes, it may be poured into the sink. Nonetheless, Bedieved, if one poured hot water into the sink, everything remains permitted, even it was very hot and was poured from a Keli Rishon.
 The reason: As the sink has absorbed Chametz, as stated above, and on Pesach we are initially stringent even regarding a Keli Sheiyni transfer and even if not Ben Yomo, and even if the Chametz absorption was only due to minority usage. [Admur 451:27 and 33; 72]
 See Admur 451:34
 As Bedieved we follow majority usage by a non-Ben Yomo Chametz vessel [Admur 451:27 and 31 and 72] and hence since the sink’s majority use is with cold products, it is therefore Kosher Bedieved.