Metal pots with an enamel covering may be koshered for Pesah; the enamel has no effect on the pots status as far as koshering is concerned.
If somebody purchased before Pesah a used utensil from a gentile, and it therefore requires both koshering and Tebila (immersion in a Mikveh), it should first undergo koshering so the taste of non-kosher food is purged, and then be immersed in a Mikveh.
If one is koshering silverware for Pesah, he may place all the silverware in a bag with holes and then lower the bag into the boiling water, rather than go through the trouble of dipping each piece of silverware separately. He must, however, shake the bag when it is inside the water to ensure that all the pieces come in direct contact with the water.
If one wishes to kosher a very large pot and does not have another pot large enough in which to do the koshering, he has two options. First, he may dip the pot into boiling water one part at a time. Meaning, he dips part of the pot in the boiling water, and then removes it, turns it around, and dips the other side. This is the ruling of the Shulhan Aruch (Orah Haim 451:11). Alternatively, one can fill the pot with water until its rim, place it on fire, and then place in it a rock that had been heated until it became fiery hot. The water will then spill over the rim of the pot, and this qualifies as Hagala (immersion in boiling water).
It is permissible to kosher meat and dairy utensils together, as long as one of them had not been used within the previous twenty-four hours. If either the meat or dairy utensil had not been used within the previous twenty-four hours, they may be koshered together. But if both had been used within that period they must be koshered separately.
