The portable sink we bought for our multivan fits the general
description of your inquiry.  It is made by RELIANCE.  We found ours at
A&H Camper Mart in Snellville, GA (770.972.2737), but I've just looked
in the index of their 425 page catalog (1997) and it is not listed.  I
found it on the parts showroom floor while I was gathering up parts to
build a portable sink unit I had designed to fold out and hang behind
the driver's seat.  It is not as full featured as what I had planned to
fabricate but works quite well for limited purposes.