MICROWAVE: There are different opinions among the rabbis, for using the same microwave for meat and dairy foods. According to one opinion, one could use one single microwave for meat and dairy, sealing or covering the foods in such a way that the steam cannot escape. Plastic wrap or a cardboard box –depending on the type of food- might be used for this purpose. Another opinion is that between meat and dairy or vice versa, one should boil water until the microwave is filled with its steam, so that the vapor penetrates the walls of the microwave rendering it Parve and suitable to be used for meat or dairy. Other rabbis would require a 24 hours waiting period -same as the oven- before boiling the water.
DISHWASHER: Rab Obadia Yosef, Shelita, allows using the same dishwasher for meat and dairy utensils, provided one is certain no substantial food particles –food residue that can migrate from one dish to another-would be present on the dishes/pots/pans. Other rabbis require running an empty cycle in between meat and dairy utensils, to clean the dishwasher of all food residues. They will also recommend to change the dishwasher racks between the cycles or to use some kind of an added base to cover the racks, because unlike an oven or a microwave, where only the absorbed vapor has to be eliminated, in the dishwasher tangible food residues might be present which makes its cleaning more difficult.