Thank you Steve!
They settle at the center of the bucket, NOT on the outside, especially the larger massed ones.
What you saw was the stuff that easily settle out, no problems there. The larger massed particles should settle closer to the center which is be explained by the total energy consideration.
I think the tougher stuff to settle out is the lower massed particles, which is easily suspended and might be kept in suspension by the movement of the water. Now, if we could slow down these particles enough, given time, they will settle out before they exit the chamber. Please note that most things have less energy when slowed down(all elses are equal).
How do we slow these things down? One way is to create an area near surfaces where fluid's velocity is slowed down by drags. Which is perfect, since these difficult particles to settle out are already on the outer edge of the vortex(by energy consideration).
I hope I am not too far off on the tangent here(puns intended).
Steve, are you in Hawaii? I went to high school in Kaneohe, HI.