I have been to several NATL FOREST areas where they allowed the dumping of GRAY WATER around the trees... They had posted signs to this as well...
I have even been to some campground where they had GRAY WATER dump area in each end of the camping spots roads. I don't know if these are tied into a sewer line or just seep into the ground. They always took all the gray water I would pour down them. I believe this one is at CLOUDLAND CANYON camp ground at Trenton GA exit on I59
Got to dig a hole for the POOP at NATL FOREST areas however or pour down the primitive deep vault bathroom setup they usually have in a central location somewhere close by...
My experiences at any rate...
Roy Ken