Probably the hardest area in the kitchen to kasher properly is the sink. The way to kasher the sink: One cannot kasher their sink unless it is made of stainless steel. 1) Do not use hot water in the sink for 24 hours prior to kashering. 2) Clean sink thoroughly. 3) Boil water. 3) Pour boiling water directly on every surface of one’s sink. Allowing the water to flow from one side of the sink to another does not suffice.
One may also pour hot water on the surface of the sink, take a hot iron and move the iron over every part of the sink surface. Alternatively, if one has an industrial steamer one may blow boiling steam over every part of the sink surface. One should set the steamer to its highest setting to ensure that it is hot enough. One has to make sure the steam turns into moisture when it hits the surface.