But, I've already bin able to make the solids collect in a nice neat little pile in my mom's pond. If I had a BD in there, it would be perfect.....I think the key is to get enough vortex action going, and an air pump helping to sweep the sloped bottm also. If the pond wasn't round, it wouldn't work....
Edit; Ok, I see your points, that some poop will what to hang up on the bottom, before getting to the BD. I'm just think'n, with the right currents, and slope....the crap should end up hang'n out in the lowest spot, in the BD 'bucket' itself....