While there are remote places where dumping is allowed. For the most part it is illegal to dump grey water at any CG. Without getting into the contents of the water.
It would create a huge mess if every camper were allowed to dump 40 gallons of water on the ground whenever they wanted.
People just aren't that smart. We can barely use the designated dump station without chaos. Dumping grey water is illegal. Do not do it. There can be fine and penalties if caught