I, too, sift the poops out and reuse it until it starts to look gritty. I use a kitchen sifter for sifting dry ingredients (I have one that is dedicated to the chins).
like the others, i also re-use dust until it gets gritty, which is usually 3 to 4 uses. i put two heaping scoops into the metal dust bowl and that seems to be enough for one chin.