I actually agree that grey water dumped or dribbled onto the ground in remote areas or even well-dispersed campgrounds poses no environmental threat whatsoever (black water? Hmmm...not gonna go there, especially for those that use chemicals). I'm just stating the fact that it CAN lead to hefty fines. At Glamis, you are prohibited from dumping grey water (BLM rules), even though you are camping in the desert, in sand dunes. Of course, BLM also requires spark arrestors on ALL BLM land, even in the desert and sand dunes where there is nothing to burn. It is easier for them to have one blanket set of rules to cover every area, rather than specific rules for specific areas. A friend received a $300 fine for dumping grey water, even though we all know that it was actually not harmful in any way, and he was in fact "dribbling" it slowly into a hole in the sand.
At one time, it was legal to dump your grey water while traveling down the highway in CA; not sure if that's still the case. And of course, the "no grey dumping" rule doesn't apply to small camping trailers that do not have a grey tank, nor does it apply to tent campers. I've been told that the difference is that once the grey water is held in a tank, "stewing" so to speak, it changes the dynamics (at least legally).