Sinks and countertops: Many people who keep kosher have two kitchen sinks. They wash dairy dishes in one and meat dishes in the other. Many also designate one side of the counter as dairy and the other as meat. Pareve foods can be prepared on either side as long as the counter is clean. If necessary, it is permitted to have one sink and one counter as long as they are kept clean.
Dishwashers: One dishwasher may be used for both meat and dairy dishes, as long as they are not washed together. If they are washed together, we are concerned the dishes will be infused with a combination of the two tastes before the soap has a chance to negate it. Some enhance the mitzva by having separate dishwasher racks (one for meat and one for dairy), and some by having two separate dishwashers.
Stovetops: The same burner grates may be used to cook both meat and dairy, because the heat of the fire incinerates whatever might spill. This is true whether the burners are gas, electric, or ceramic. If a dairy pot is on one burner, and a meat pot is on another burner, one must make sure to leave space between them so that anything boiling over from one will not splash onto the other.
Ovens: It is common to have two ovens (or one oven with two compartments) and to designate one meat and one dairy. Using the same oven for both meat and dairy consecutively is permitted, as long as there are separate baking dishes, pans, or trays. The oven should be kashered in between uses by heating it to its highest temperature for half an hour. Many people swipe out the oven first. If dairy food in a dairy pan was accidentally baked in a meat oven, the dairy food is kosher, since we assume the two tastes did not combine together.
Microwaves: One may use the same microwave consecutively for meat and dairy. This is on condition the foods are not placed directly on the turntable, and that they are covered to avoid steam penetration from the microwave. Small holes in the cover are acceptable. In pressing circumstances, one may heat food in a microwave that has been used for non-kosher food, as long as the kosher food is on its own plate and is well-wrapped on all sides (even if an opening allows steam to escape).
Kashering a kitchen: These laws are similar to kashering for Passover and will be explained later (30:9-10).