The human waste from one family using an outhouse is minimal compared to the poop from one cow. Say a person poops 6 to 8 ounces a day, maybe 120 to 150 pounds a year. It enters the outhouse one poop at a time, and there are soil organisms, worms, etc., that are constantly at work to break it down. Even for a family of 4 or 5, the input averages 2 to 3 pounds a day. Yes, that can outrun the breakdown process, but only by so much. Normally outhouses are cleaned out every few months, and the proceeds (!) spread or disposed of in some naturally fairly sanitary way. One outhouse on a few hundred acres is a minor detail compared to a herd of cattle or pigs.

The Amish poop?

Regular poop is harmful. Amish poop, however, is quite the opposite. Before diffusing into the waterways, Amish poop helps raise a barn, sews a couple of quilts, and processes a few blocks of cheese as a way of giving back to the community that spawned it. Regular poop has no appreciation for such things.

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"...I once ate a roadkill possum that had been raised on a diet of carp. I cooked it over a fire fueled with old tires and dog shit. [My fart] put to shame the sewers of Calcutta."
- ChiefThunderbutt

You're right VD, and every Amish poop has one of those reflective triangles at the end.

Get 'er dung.