Directly from Kyle:
My thoughts for the Phantom Shithouse's back story is that a backwoods part of the Ozark's where greedy corporations started dumping their toxic waste also happened to be inhabited by a hillbilly family. The toxic waste leeched into their water supply and food creating some pretty unusual trips to the outhouse. Eventually the bacteria and toxic "waste" created a symbiotic hive mentality and uprooted from the hole, taking the outhouse right with them to exact revenge on corporate greed and any who dare stand in its stinky wake!
Kyle is also responsible for the above illustration, showing what happens when Travelers don't flush. Thank you to Kyle and Ralph for bringing this hilarious pile of wood and poo to life!