another option is to throw a pump or powerhead in the sump to keep the crap floating in the water. then direct it to the skimmer to be removed. you may need a bigger skimmer if this is a problem.
Of course I've seen them poo P.P. it's mostly sand after it's passed through their very efficient digestive track. Once per ounce they are one of the best clean up critters out there in my opinion.
hth
Max
