The hagala water must actually be boiling, and this is a sine qua non with regard to utensils that have absorbed ĥametz as a kli rishon on the fire. As we have learned, the practice, le-khatĥila, is to perform hagala on all utensils in a kli rishon over fire.
The entire utensil must be submerged in the water for a few seconds. Sometimes the immersion of utensils cools the water to the point that it stops boiling. In this case, the utensils should be left in the water until it returns to a boil.
If a utensil cannot be immersed in its entirety into the water, it can be immersed one half at a time (SA 451:11).
Furthermore, when immersing two utensils into the boiling water at one time, one should shake the utensils to ensure that the boiling water circulates between them (based on SA 452:3-4).
Common practice, le-khatĥila, is to rinse the utensils with cold water after hagala, so that the hot water does not remain on them and cause them to reabsorb the taste released during hagala. This is not essential, however, since hagala is normally performed when the utensil is not ben yomo or in water that has a foul taste, so that even if the utensil reabsorbs the taste of the water, it will not be rendered un-kosher (SA 452:7; MB ad loc. 34). Therefore, one should not rinse utensils with cold water if this is liable to damage them. Likewise, if for some reason it is difficult to rinse a utensil with cold water, one need not make an effort to do so.
Though some people have reservations about performing hagala on their utensils, the procedure is actually quite simple. In brief: First, one cleans the utensil and waits twenty-four hours after it absorbed forbidden food. Next, one immerses the utensil in boiling water. If it is possible to take it out and rinse it immediately in cold water, this should be done, but if it is difficult, one may extinguish the fire under the pot of boiling water, wait for the pot to cool down somewhat, and then pour out the hot water, and rinse the utensil a bit in cold water. One may use any pot in the kitchen for hagala, provided that it has not been used for cooking in the previous twenty-four hours.