How does one maintain a kosher kitchen sink?

The surface of the sink should not be used for both meat and dairy dishes. Ideally, a kosher kitchen should have two sinks: One to wash meat dishes, and the other for dairy dishes. When it is not feasible to have two sinks, one should presume the walls and floor of the sink as being non-kosher. Therefore, no utensils should be placed directly on those surfaces. Rather, one needs to have separate sink inserts (usually plastic racks and bowls) for meat and dairy use. Clearly, one must have separate sponges/dish racks/etc. for both meat and dairy. If practical questions arise, please do not hesitate to consult a competent authority in Jewish law.