The Nassarius Snail is a little snail with a big appetite. This hungry critter glides through your aquarium foraging for food. The Nassarius Snail is an efficient scavenger and detritus eater and is the perfect member of your reef aquarium cleanup crew. You will be pleased at how quickly a small group of Nassarius Snails will clear detritus, uneaten food, decaying organics, and fish waste."
This was taken straight from liveaquaria and is one of several sources that say they consume fish waste and decaying organics.