Contrary to what people are suggesting, Galactus is a force, and only made of energy, his "body" isn't a life form, closer to an avatar. He doesn't eat either, he just consumes energy and uses it as power. There's no waste in pure energy, it's not like food, and he also doesn't have a real body, so I would assume not.
He probably doesn't, whatever he consumes probably just disintegrates in his stomach or something. If he did imagine a cosmic turd floating through space colliding with planets and stinking so bad that its smell spreads across the universe.
Or he shrinks himself first, then does his thing. Small poop.
*Note to humanity; if we ever venture further in space, don't land on the brown planets.
@supersomebody @monster @galactus