Funny how what is considered "green" varies depending on the situation. Seems to be the consensus in this thread that dumping is not green. However in CA, I know people who have modified their home's plumbing so that sink and shower water drains into a 250 gallon tank that they then filter and use for watering and washing the car etc. Considering CA's drought, what they are doing is very green.
For me personally, when we had a pup with no holding tank, we did sometimes let the water from the sink drain on the ground depending on the situation, ie. no puddling, no running into someone else's campsite or into a stream. Pretty much it needed to be very porous soil. Also we only use all natural soap, so it was basically just water with no smell whatsoever.
Now that we have a TT, we just use the holding tank and dump at the dump station. If the tank fills up before we leave, I have a 30 gal portable tote with wheels to haul it to the dump area. I have however used gray water from my holding tank to water the lawn and landscaping at my house. It does have an odor though, so I'm looking into finding a way to filter it. To me, if done properly, reusing gray water for irrigation is far greener than dumping it in a sewer.