Ok. So, I gave this a try. Wasn't terrible, but the best result that I could achieve was to reduce concentrate volume by a little more than half. Seems like I hit an inflection point where there was a tradeoff between removing more black sands or losing some fine gold. The lightest/most fine black sand material washed out very nicely but I ran into the aforementioned problem once I needed to adjust water flow to start removing coarser material. ...Perhaps, I just needed to spend time tweaking things to get desired results.
Might give it another shot at some point in the near future. I don't have a blue bowl or other such equipment, so would be nice if I could use this much less expensive approach.