This achievement is super easy to get, just takes a little time. It's best done by setting up some farms and putting an animal or two in each. The important thing is to NOT hire someone to take care of the farm, as they will auto clean the place.
After you have some farms set up (at least 2 with no farm caretaker) craft some Traveler's Knots (2 Vine, 1 stone). Now just fast travel between your farms and collect all the poops. Then walk away for 5-10 minutes or do some fishing or a quest. Then fast travel to the farms again. Really simple, just make sure you have something to do in between poop spawns.