We have this same model as the OP. At first I was surprised to find the same thing with the outdoor sink, however now I'm kind of glad that it doesn't drain into the grey tank. My grey tanks take longer to fill as the kids can use a lot of water to wash as they pay no regard to filling up the tanks ;). We limit the outdoor kitchen sink use to washing hands and light rinsing off of things as not to cause odors. To me this is no different then what tenters do. They don't have grey tanks to drain their washing water and they wash ALL their dirty dishes and hands and whatever else, letting it fall to the ground.