The kitchen sink and countertops are generally used with cold foods, but sometimes hot liquids spill onto them from a kli rishon, and in such cases their usage is at the level of irui mi-kli rishon. And sometimes burning hot quiches and pastries or pots from which sauce is overflowing are placed on them. In these cases, their usage is at the level of “kli rishon removed from the flame,” which is kashered by pouring boiling water over a white-hot stone.
If it were not difficult, it would be proper, le-khatḥila, to kasher them by pouring boiling water over a white-hot stone, but since this is difficult to accomplish, one may kasher them le-khatḥila by pouring boiling water over them, in accordance with most of their more intense usage. Before pouring the hot water over them, one must clean them well with soap and water, paying attention that no food residue remains in cracks. One must then dry the sink and countertop before pouring, so that the boiling water touches them directly and is not cooled by any cold water on their surface. For this reason, one first pours the boiling water on the bottom of the sink, then on its walls, and then on the countertop, starting with the areas closest to the sink and moving further away.
In home kitchens, the custom is to kasher the sink and countertops using water that was heated up in an electric kettle (“kumkum”). Since the kettle is not large enough to heat up enough water all at once, the kashering is done in stages; in each stage, water boiled in the kettle is poured over one area. If the poured water trickles over to an area that has not yet been kashered, one must squeegee it away before pouring more boiling water from the kettle over it.
Instead of pouring hot water, one may also cover the countertops with oilcloth or foil and either place a plastic insert in the sink or line it with thick foil. Those who are stringent clean and pour hot water over the countertops and sink and also cover the countertop with oilcloth or thick foil and either place a plastic insert in the sink or line it with thick foil.
Sinks have the same status as countertops. However, if the sinks are made of porcelain, some are concerned that it has the same status as earthenware, in which case hagala is not effective. Therefore, they require the placement of a plastic insert or lining the sink with thick foil to serve as a barrier between the sink and the kelim placed therein (Ḥut Shani, Pesaḥ 10:17; Sidur Pesaḥ Ke-hilkhato 8:1, which adds that a stainless-steel sink is kashered by pouring boiling water over a white-hot stone). However, porcelain sinks are made very well, and their coating is as impenetrable as glass. Therefore, they can be kashered (see below, n. 11) le-khatḥila by means of pouring boiling water, and, when necessary, by rinsing. (Ḥazon Ovadia, Pesaḥ, p. 151 rules that one may kasher by pouring boiling water; Or Le-Tziyon 3:10:11 states that one may kasher by rinsing or cleaning with cold water, but the custom is to pour boiling water.)
One may kasher sinks and countertops with a steam cleaner, as long as it is high-quality, and it is as effective as pouring boiling water on them. However, burning alcohol on sinks and countertops is not as effective as pouring boiling water, as is evident from the fact that it does not heat up the countertops like pouring boiling water does.