I have the intake for my filter is sticking out of the sand in the corner of the tank, actually one intake on each corner, and then I have directional nozzles that are pointed down from the center, it creates a nice swirling current that sweeps most of the poo into the intake eventually. Oh and I also have airstones in the corners as well, they are connected to a powerful air pump that aid the swirling current.
I have had a headache with the same problem for a long time. my oscar's large poops were always the ones left on the sand. A powerful filter and air pump seem to be the working combo for this.