1. Once, the halachos of hag'alah took up a major portion of the Pesach preparations. Most people did hag'alah on all their utensils for Pesach. Nowadays, however, people generally have separate Pesach utensils, as the poskim write regarding certain things, that it is best to buy new for Pesach (מ"ב סקי"ט ). As a result, hag'alah is not as common as it once was. Still, there are things on which hag'alah is done even today. Also, hag'alah is used all year round for issur v'heter.
"Kebol'o Kach Polto" [As is the Absorption, So is the Expulsion]
2. Hag'alah. The removal of absorbed matter from a vessel must follow the method through which it was absorbed. Therefore, if matter got absorbed through water or some other fluid, it must be extracted through a process whereby the vessel expels the absorbed matter into water, which nullifies it. This is called hag'alah.
3. Libun is the process of using fire to burn out absorbed matter. It is used if a substance was transferred from the food into the vessel without the presence of liquid, as will be explained below.
4. Kli rishon. Based on the rule of kebol'o kach polto, a utensil used as a kli rishon, i.e., one that is used over a fire, for example, a pot or a spoon used to stir food over a fire, must be kashered in boiling, bubbling water, (רמ"א תנ "ב ס"א ) in a kli rishon specifically (שו"ע תנ"א ס"ה ), over a fire (מ"ב סקל"ו ). If it is used as a kli rishon not over a fire, hag'alah may be done in boiling water in a kli rishon without a fire (פמ"ג משב"ז סק"ט ).
5. If the absorbed substance was kosher, e.g., meat or milk, some permit hag'alah to be done in a kli rishon even not over a fire (שו"ע שם ס"ג, ומ"ב סק"כ, שו"ת שבט הלוי ח"ו סי' נ"ו אות ד'). Some also apply this leniency to chametz, since there are those (עי' מ"ב סקכ"ח ) who hold that absorbed chametz prior to Pesach is considered heter, not issur (שו"ע הרב סכ"ה ).
6. Pressure cooker. Even utensils used with heat levels above water's boiling point [100 °C], e.g., pressure cookers, or with oil, which gets much hotter than that, may undergo hag'alah with boiling water, as Chazal did not differentiate between different heat levels; they only focused on the heating method (שו"ת מנחת שלמה מהדו"ת סי' נא ).
7. Irui kli rishon. When only the external surface absorbed something ["kedei klipah"], e.g., something was poured from a kli rishon onto it, or something hot went on top of something cold [based on tata'ah gavar (שו"ע יו"ד סי' צא ס"ד )], hag'alah may be done by pouring boiling water from a kli rishon in a continuous stream (מ"ב סקמ"א ); a kli sheni does not suffice (שו"ע ס"ה ) even bedieved (מ"ב סק"מ ).
8. Kli sheni. A utensil used as a kli sheni (שו"ע שם ), i.e., one that is never used over a fire (מ"ב סקל"ז ), may undergo hag'alah in a kli sheni. This is done by pouring boiling water from one vessel into a second vessel, and then placing the utensils requiring kashering into the second vessel.
9. Plates or cutlery, despite being used for the most part in a kli sheni, are sometimes [at least for a significant minority of the time (פמ"ג א"א סקכ"ב )] used in a kli rishon. The poskim debate how to kasher them. The Mechaber holds that we follow their majority usage and they may undergo hag'alah in a kli sheni (שו"ע ס"ו ) unless they may have been used (חזו" א סי' קי"ט סקט"ו ) within 24 hours with chametz in a kli rishon (מ"ב סקמ"ו ).
10. The Rama holds that they should be kashered in a kli rishon to cover their minority usage (רמ"א שם ). However, bedieved [i.e., one cooked something with it (שו"ע הרב סכ"ח ול"ג )] one can rely on the Mechaber (מ"ב סקמ"ז ).
Cleaning Prior to Hag'alah
11. Hag'alah only works on absorbed matter; not on intact matter. Therefore, before hag'alah, one must clean the utensil from any substances (שו"ע ס"ג ) and remove any grime from its crevices.
12. If there is a substance which cannot be removed, one must first burn it out through libun, and then do hag'alah (שם, ומ"ב סקכ"ה ). Libun kal suffices [see below, 30-31] (רמ"א ס"ד ומ"ב סקל"ג ).
13. If fire will ruin the utensil, one may pour bleach on the substance and then do hag'alah (ספר הגעלת כלים פ"ו סעיף ד ).
Silver
14. Strictly speaking, utensils made of silver [e.g., bechers, cups, plates, etc.] that are used all year do not require hag'alah for Pesach, as they are not used with heat. Still, they are sometimes cleaned with hot water in a sink containing chametz utensils. Therefore, many kasher silver.
15. Often, silver utensils have nicks which accumulate black tarnish. Also, many cups have a groove under the lip which accumulates grime. In general, any dirt must be removed before hag'alah. However, since silver does not really require hag'alah, the hag'alah may still be done with the tarnish in the crevices.
16. Candlesticks do not require hag'alah, since they are not used with food. However, if they are on the table throughout the year, it is customary to cover their base, since many people avoid placing anything that was on a table with chametz on the table on Pesach. They may be covered with saran wrap/cling film, which looks nicer than aluminum foil.
Urn
17. Stainless steel water urns are not generally used with chametz. However, since they are in the kitchen with chametz, are used to add water to a chametz dish, and sometimes have chametz [e.g., challah] placed on them, they can easily absorb chametz matter. Therefore, they must be kashered for use on Pesach.
18. Often, scale forms on the inner walls of an urn. Hag'alah may not be performed in this state, out of concern that there may be chametz under the scale (שו"ת אבן ישראל ח"ז סי' כא ). Therefore, just like rust must first be removed (מ"ב סקכ"ב ), scale must also first be removed. [This can be done by boiling vinegar in the urn.]
19. Q: I lost the lid to my Pesach urn, so I want to use the lid to my regular urn. Sometimes I heat up challah on top of the urn. Does the lid need hag'alah since it is heated with water, or does it need libun since any chametz it absorbed was not through water? A: Since it absorbed chametz directly from the challah, it requires libun. However, bedieved, if this will cause great trouble, hag'alah works, as it does bedieved for anything for Pesach (below 31).
Women's Rings
20. Often, women wear rings while making chametz. It is possible that chametz got absorbed into them or that there are actual bits of chametz stuck to them. Therefore, they should be removed during the preparation of food for Pesach. Some women clean them and perform hag'alah before Pesach through irui kli rishon (above, 7).
21. If a woman did not clean her ring and it touched hot food on Pesach, the food remains permissible, since it is mostly used with cold food, and since people don't generally touch food so hot that the hand recoils (מו"ר בשבט הקהתי ח"ו סי' קצ''ג).
New Utensils
22. In Eretz Yisrael, many do hag'alah on every stainless steel vessel they buy all year round out of concern that oil from a treif animal was applied in the making of the utensil (משמרת שלום יו"ד סי' קכא סקי"ב, חזו"א יו"ד סי' מד סק"ד ). They also do hag'alah on any new utensil they buy for Pesach out of concern for chametz (שיעורי קנה בשם פ"ד אות ד ).
23. It should be pointed out that this is just a chumra. It is highly implausible that treif oil was applied, and even if it was, it certainly got ruined in the factory machinery. There are other reasons this is not necessary (שו"ת משנה הלכות ח"ז סי' קיב ), especially since today, usually only vegetable oil is used. In most communities in the rest of the world, they do not do this.
24. Also regarding the concern of chametz, since we buy utensils from stores, and not secondhand from Goyim, there is no reason to be concerned they were used with chametz.
25. Two vats. Since toveling new utensils is only a chumra, in public areas for hag'alas keilim there should be two vats; one for new utensils which practically have no issur absorbed, and the other for utensils that may have chametz absorbed inside. This prevents the new utensils from absorbing anything from the old utensils which would defeat the purpose of doing hag'alah. Bedieved, the utensil would be permitted.
Pot in Which Hag'alah is Done
26. When hag'alah is done before the 5th hour on Erev Pesach [which is suggested, to avoid Erev Pesach pressure], it can be done in a Pesach or chametz pot. If it is done after the 5th hour, if it is in a chametz pot, that pot must first undergo hag'alah and the utensil being koshered cannot have been used within 24 hours, unless the koshering water contains 60 times the wall volume of the utensil being kashered (שו"ע סי' תנב ס"א ובמ"ב ).
27. The vessel does not need to undergo hag'alah all at once. The hag'alah can be done part by part as long as it covers everything.
