http://www.ok.org/Content.asp?ID=115
The Sink: Separate sinks for washing dishes and preparing foods are
recommended. If the two sinks are adjoining, there should be an
effective separation between them so that no water or food splashes
from one sink to the other.
If there is only one sink, it may be used after it has been completely
cleaned, but the inside of the sink should be regarded as non-kosher.
No food or dishes should be put directly into non-kosher sinks. There
should be separate dish pans and slightly elevated racks under the
dish pans for both meat and dairy. Similarly, two sinks which were
used before the kitchen was kosher should also be regarded as
non-kosher, unless they are stainless steel and were koshered. If the
two sinks were koshered, one should be designated for meat and one for
dairy.