Lol! Yes, they do, but the deal is, they take in waste as food, then reduce its volume considerably. What they excrete is immediately processed by worms and bacteria.
So you can think of them as the tank's trash compactors, and you can have as many of them as your tank can sustain off the waste of other creatures...not an infinite number, if you wish to have other things, because pretty soon you'd be specially feeding THEM, but you'd be surprised how tightly inverts can pack a dirty tank and keep in business.
