Written by Rabbis Eli Gersten, Yaakov Luban, and Moshe Zywica of the Orthodox Union
Since one might have washed their kiddush cup throughout the year together with hot chametz, (e.g. in a sink or dishwasher), it should be kashered with hagalah, a kosherization process with boiling water.
The cup should be scrubbed well, with extra attention given to any crevices, and then the cup should not be used for 24 hours. To kasher, one should submerge the kiddush cup into a pot of boiling water for 10 seconds and then rinse off the cup with cold water.
The pot used for kashering may be a chametz pot that had been thoroughly cleaned and not used for 24 hours.
First one fills the pot and brings it to a boil. (There is no need to overflow the pot, unless one plans on using the pot for Pesach). That water is spilled out. The pot is then refilled, the water is boiled, and may then be used for kashering (see Taz O.C. 452:10).
Silverware requires kashering with hagalah because it is used throughout the year with hot chametz. It must be cleaned, left unused for 24 hours, and then immersed in boiling water as described above.
If kashering a knife with a handle and blade that are separate pieces and the fit is not tight, we are concerned that there may be chametz in the space between the handle and the blade. It is also difficult to properly clean the blade of a serrated knife. One can address these concerns by passing these areas, or any other cracks in the silverware, through the flame of a candle for a few seconds before the kashering takes place.