For the purposes of hagala, any kitchen pot can be used, as long as it is clean. The hagala water must actually be boiling.
The entire kli is left submerged in the water for about three seconds. Le-khatḥila, the custom is to rinse the kelim in cold water immediately after hagala, but this is not an absolute requirement (SA 452:7; MB 34). Therefore, when it is difficult to rinse the kelim in cold water, there is no obligation to make an extra effort to do so.
Sometimes the immersion of kelim cools the water to the point that it stops boiling. In this case, the kelim should be left in the water until it returns to a boil. If one inserts two kelim simultaneously into boiling water, one must shake the kelim to ensure that the boiling water circulates between them (based on SA 452:3-4).
If a kli cannot be immersed in its entirety into the water, it may be immersed one half at a time (SA 451:11).
Many have the custom le-khatḥila to perform hagala in boiling water even on kelim that were used for irui or as kli sheni (above, section 6).
In brief, this is the procedure of hagala: First, one cleans the kli and boils water in a large, clean pot. Any kli that requires hagala is then inserted into the boiling water for about three seconds. The kli is now kosher. The custom is to add liquid soap to the hagala water or to wait 24 hours from last use with ḥametz or forbidden foods before performing hagala; for kelim that are not clean, it is obligatory to do so. Le-khatḥila, the kli is rinsed in cold water after hagala.
The Rishonim also wrote that one should rinse the kli with cold water after hagala, to remove from the kelim what they released and so that the heat of the water does not cause the taste released during hagala to be reabsorbed or get re-stuck (Rambam, Raavyah, Rashba, and many others; Me’iri states that instead of rinsing in cold water, one may dry the kli to wipe off anything that was released and then stuck loosely to the surface of the kli). However, the Rishonim wrote that rinsing in cold water is not essential for the hagala to be effective, as it is not mentioned in the Talmud. Aḥaronim explained that this is because the custom is to perform hagala on kelim that have not been used for 24 hours. (See MB 452:34.)
. Although the custom of Ashkenazic communities and some Sephardic communities is to avoid using hagala to switch kelim from meat to dairy and vice versa, when kashering kelim for Pesaḥ one may switch them from meat to dairy even le-khatḥila (Ḥatam Sofer, YD 110; see Peninei Halakha: Kashrut 33:9, n. 11).