I boondock almost exclusively and am very stingy in the water department so don't generate big quantities of greywater. The little I do make goes into the ever-present fire pit- no better treatment for it than the thick layers of ash. All grease/food particles etc are of course consumed by fire- or, as we like to say "converted to energy". ;)
If camped during no-burn time, I stir the water in. The ashes break down grease and also have a neutralization effect that kills odors. Thus nothing left to annoy folks or attract varmints.