This is a very interesting project. I'm glad it was brought back up. jdizzle3id brings up a good point. By spinning a drill bit or something similar inside a PVC
tube, it will raise up sand without needing a big footprint. As for sand falling out of the contraption, why can't the bottom be a funnel type unit, pulling the whole substrate of sand in as the sand falls? Sure you'd have to level out sand, but I can't imagine you'd have to do it any more than during a weekly PWC
Did this ever get done? I'd love to see it.