Well, I'm reading this with interest wondering what could be done. . . We're lucky living in Vermont as we have a well and an endless supply of water we don't have to pay for. So, pretty much--in the summer--after the pond gets filled with pollen, cattails and the like-our ducks revert to just hanging out on the edges of it and using the small pools. But, like I said--no problem to empty them out. In the winter, we put a heater in the pools since they still have to be able to dunk themselves to get clean. Those crazy ducks don't care what the temperature is outside. I don't know how a filter would ever ever work with all the duck waste that comes out of their little butts, but I'm watching the posts here. 
