Wouldn't dream of dumping it. It is all soap and whatever is washed off the dishes however, never any grease.
One way, I saw to help loosen clay ground and help grass is to spray a solution of baby shampoo, in a hose end sprayer, on the ground. Let it set and then water it in good with a hose. Repeated treatments loosen the clay.
Might be one reason GrandMa's place didn't have tight soil anywhere.
Wash the dishes or baths and it got thrown into some of the garden area.
:)
I'm not sure how strong the dish soap, clothes washer, shower soap concentration would be in our gray tank. Would help the grass, it seems, but I wouldn't want to set up camp, in a pool, of soapy water nor smell the stuff. If you do please, use a lot of gray water deodorizer and, don't use that stinky shampoo, my wife uses and let me know so I can go somewhere else.