In the beginning people just pooped on the ground, but eventually they realized that burying their poops was a good idea. Over time various methods of dealing with poops developed with the outhouse being a major innovation somewhere along the way. Today we have septic tanks and sewage systems which use pipes to take the poops from individual toilets to a waste water treatment plant. At the bottom of the Grand Canyon at a place called the Phantom Ranch exists a cluster of buildings which include residences, rental cabins, restroom facilities, and a restaurant. The toilets installed in these buildings are connected to sewage pipes which take the poops people produce down to a treatment plant and at that plant the poops (and whatever else winds up in the sewage) gets processed and then ultimately put into drying beds and then packaged up to be flown out of the pristine park to a landfill somewhere. It's a messy job, but someone's gotta do it!