I got this one from Amazon based on some input either here or T4R.org
My intention is to build some low storage into the 4Runner with a slide for my cooler. I want to put a pull-out shelf under the cooler with an opening for the sink. It collapses so it won't take much height. I'll cut the handle attachments on it for a lower profile. Then I'll just lift it out to dump it.
I've seen a few people use a medium to large stainless steel bowl as a sink. It can be used as a portable or built in to a counter. For a permanent install, you can cut a hole in the bottom and install a sink drain routed outside or to a portable holding tank.