We have seen that in order to kosher a pot used to cook ĥametz (barley soup, for instance), it must be immersed in boiling water. When the boiling water inundates the vessel on all sides, it extracts the taste of the ĥametz from it. Based on the principle of ke-bole’o kakh polto, it ought to be possible to kosher such a pot by simply boiling water in it, and the pot will expel the taste just as it absorbed it. However, during the course of the year some cooked foods certainly boiled over the sides of the pot, causing the absorption of taste along the pot’s rim. The taste would not be released by water boiled inside the pot. Thus, in order to kosher such a pot for Pesaĥ, it must be completely immersed in a large vat of boiling water.
If one cannot find a vat large enough for immersing the pot one wishes to kosher, the poskim suggest the following: fill the pot you wish to kosher with water and bring it to a boil. At the same time, heat a stone so that it becomes scorching hot. When the water boils, insert the scorching hot stone into the pot. This will cause a lot of water to spill over the sides of the pot, koshering its rim and its outer walls.
This method is effective where a vessel has absorbed ĥametz through overflow, but if a pot was inserted into another pot and absorbed taste, it has absorbed in a kli rishon, and hagala by the overflow method is not effective. Instead, it must be koshered through complete immersion in boiling water (SA 452:6; MB ad loc. 31).
It is difficult, however, to heat stones in this manner in domestic kitchens. Therefore, a possible alternative is to boil water in a small vessel, and when the water in the large vessel begins to boil, insert the small vessel into the center of the larger vessel. This will cause the water in the larger vessel to overflow and kosher its rim and outer walls.
If the pots have removable handles, it is proper to remove them and perform hagala on them. However, if the handles were not removed, and one cleaned around them with plenty of soap and then performed hagala on them, the pot is kosher.
Another problem is that many pots have a lip along the rim and on the edges of the cover where food sometimes gets stuck. The preferred practice is to heat these areas with a blowtorch in order to incinerate the residue found there. However, one need not be meticulous about this, because the pot goes through enough rinsing and cleaning with detergents to render the taste of any residual food foul and unfit for a dog’s consumption, so that it does not even have the status of ĥametz. Therefore, if a blowtorch is used, its flame should not be directed at one place for too long, because doing so might damage the pot’s nice appearance. When necessary, one who cannot perform light libun on this lip may suffice with hagala.
. We once examined the lip of a pot, and the substance contained in it was black, ugly, and extremely foul-tasting. Therefore, even without libun it is not forbidden. Similarly, whatever builds up around the pot handles is exceedingly foul, so even if one did not remove the handles, the hagala is valid. Nevertheless, to be on the safe side, one should rinse that area with a lot of soap. Regarding hagala on a large pot that does not fit inside an even larger pot, I have seen it suggested that one cause the water to overflow by pouring boiling water into it from an electric kettle that is still connected to a power source. My solution is better, though, since with the pouring method, the water cools down slightly, whereas in my method, the whole pot boils and becomes a kli rishon without cooling down at all.
Regarding milk and meat: Sometimes some liquid from a boiling dairy pot splashes onto a cold meat pot, and we consider the outer layer of the meat pot to have absorbed some dairy taste at the spot that was hit by the liquid. The way to kosher the meat pot is by pouring boiling water on it, and since we are dealing with a very small absorption, one need not even wait twenty-four hours, since it is possible to pour sixty times the amount absorbed on the spot. If one is concerned that there is not sixty times the absorbed amount, he may mix soap into the boiling water, which will befoul the absorbed taste. On the other hand, if the meat pot contained hot food when it was splashed by the dairy liquid, the pot needs to be koshered in boiling water. One should consult with a halakhic authority about the status of the food in the meat pot, since sometimes it is sufficient to have sixty times the amount of dairy liquid, while other times there needs to be 3,600 (sixty times sixty) times the amount of splashed liquid.