Q. I understand it is possible to kasher glass which has not come into contact with hot food by soaking in water for 3 days and changing the water every day. Does it have to be soaked on the outside as well as the inside? Does the water have to be changed at the same time every day? Last time, I soaked it in a bathtub. If I do this, does all the water have to be 100% emptied and what if some items fell over, leaving an air bubble?

A. There are different opinions in regards to kashering glass utensils for Pesach. The Mechaver in O.C. 451,26 requires only good cleaning and rinsing, as glass does not absorb. For Ashkenazim, Remoh (ibid.) is stringent, and he considers glass made from sand, to be similar to earthenware utensils, that can’t be koshered. Mishne Berurah (ibid. 156) advises to acquire new glass utensils for Pesach when possible. If new glasses are not an option, milui veirui, could be done. This implies filling their inside only completely with water, keeping each time the water for at least 24 hours, (regardless of the time of day), and then emptying them totally and replacing with fresh water. When done thrice, it would render them kosher, especially if they were not used hot. You could shorten the process by kashering in a boiling pot, if you are not afraid that the glass utensils may crack. (M’adanei Shmuel on Kitzur Sh.A. 116-35, Sdei Chemed 4,5,30).

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