Dumping a full tank of grey is not nice to the neighbors. We camp at one place every year where there's room, but no sewer. A "honey wagon" comes along for the black tanks, and the grey tank is always open, slowly running when we use water, with a hose to direct it to a low spot away from our camp site. There is absolutely no nuisance from this, and no concentration of anything.
News flash... there are animals crapping in the woods, or eating other dead animals..... and so on and so forth.