"Number two... is more challenging because you're trying to hit a pretty small target," astronaut Peggy Whitson told Business Insider.
The poop is sealed inside a plastic bag and hauled off the next space trash day, Whitson said. When it's too full, astronauts must "put a rubber glove on and pack it down." That's what happens when the ISS toilet is working. When it malfunctions, astronauts will occasionally have to deal with floating poop.