Outside Shower Enclosure

Great Smokey Mountains NP regulation:

Waste Water
Dish water and bath water must be drained at utility sinks or dump stations, not on the ground. Do not wash or bathe in streams or at water fountains. RV sewage should be drained only at a dump station. Showers and utility hookups are not available in the park. Showers may be available in nearby towns.

Capital Reef NP (Utah) regulation:

Bathing/Dishwashing:
Wash dishes, bathe, and use only completely contained solar showers at your site. Washing of any kind is not permitted at spigots, drinking fountains or the RV dump station. Do not wash dishes in the restroom or gray-water sinks. Water from dishwashing, bathing and solar showers must be collected and deposited in gray-water disposal sinks.

Those are just the first two examples I found.  My point is, despite what might seem to make sense or to be reasonable there are sometimes regulations that apply.  The NP Service probably has their own rationale, but I think the rules are based less on consideration of fellow campers than of the environment.  All kinds of animal behavior, not to mention health, can be affected scents and pathogens of human activity and waste, even if it seems trivial or is invisible to us.  Of course, in cluster campgrounds, the problems are easily compressed and concentrated to the point that they can be annoying or unhealthy to humans too.

And let me say this about boondocking, picking a nit perhaps.  We camp in the Smokies and Outer Banks National Seashore campgrounds more than anywhere else, and there are no hookups at all in those campgrounds, so if you stay there, you boondock.  These campgrounds aren't as tightly packed as a lot of places I've seen, but let's just say it's still not hard to have an annoying neighbor.  Plus, quite often in season, there is someone setting up in the site I just left before I leave the dump station.  If it's me moving in, I don't want to find a puddle of someone's bath or dishwater.

On the other hand, I've been to those dispersed campsites too that Furpod referred to.  There are still environmental concerns even if no one will camp in the same spot for another two years.  Leave no trace is generally the rule to go by.  Again, it really, really gripes me in those kinds of places to have to deal with, or even see, someone else's trash or waste that wasn't carried out our buried properly.  I figure the reason people go to those places is to enjoy nature in its pristine state.  Unless we go to the necessary effort to protect those places the stress of all the additional people who like to camp nowadays will make places worth going to harder and harder to find.

All that said, there are places remote enough that even I figure if a bear can do it in the woods, I can too.  But I bury my crap and don't use soap or shampoo if I find it necessary to bathe in a lake or stream.  I'm talking about places Pods don't (can't) go.

TT

Pahaque makes one of the stand up portable latrines like Cabela's. They have a use, where legal to use and if boondocking. We used to set one up in base camp when we mule deer hunted in AZ. I wouldn't use one in a campground nor use my outside spray wand as a shower in a campground. Really about common sense.