Some time back I researched this very subject and almost bought an outdoor shower with a water (gray) collection basin. It would have been perfect for camping in the primitive campgrounds with limited or no facilities or boon docking in remote locations. I had a pop-up camper with no indoor facilities at the time. If I can find it again I'll post a link in this thread. There are many places that address gray water disposal and some have specific dump locations….those are usually developed campsites that ofter have toilet and shower facilities. Even the more primitive campgrounds usually with only pit toilets will have some kind of statement as to the disposal of gray water and thus outdoor shower water. If you can contain it and dispose of it to their satisfaction you would be good to go. If unclear I'd talk to a host or Ranger to be certain.