I have read on this website that one may kasher a sink or countertop. However, the reality is that it is impossible to pour hot water over all of the counter top or sink. Counter tops have backsplashes which cover the back inch. The lip of many sinks, as with granite countertops, are under the countertop. In addition, sinks have parts attached to them for draining, faucets, handles, or soap dispensers. Why does this not affect the kashering of the sink or countertop?
Thank you for your question.
You are bringing up an interesting point.
The reason it is permitted to kasher a countertop, or a sink etc. even though it has parts that cannot be accessed, is because we only have to ensure that the water touch all of the external parts of the vessel we are koshering. The reason we need total access to the surface we are koshering, is because if the trief taste entered the vessel and is now covered with dirt, clay, or rust, then the water doesn’t have access to the trief taste the we are trying to purge. However, if the vessel was made this way, and was bound together before the trief food got there it isn’t a problem. If any trief taste managed to get there, the same way it got there with the heat it had, the koshering will pull it out. The Shulchan Aruch (O:CH 451-13, M:B 73) discusses a case that someone attached a metal patch to a pot, that the pot cannot be koshered until the patch is removed. However, if he patch was attached to the pot before it was used, there is no need to remove it. Our case is similar to that.