Carl, in terms of the DC, I use it for a combo machine (saw, shaper, jointer, planer) and router table only. None of these produce significant amounts of fine dust compared to a sander as you know. About all I can offer in terms of separation is I've filled the 55 gallon drum 4 times over the last 5 months. During that time I've collected about a cup of fine dust in the poly bag. After I clean off the filter with air this produces about 4 or 5 cups each time (have cleaned it twice so far). Your estimate of 1-2 cups per 30 gallons might be about right if I used a sander, otherwise its a bit high. I use a Festool vac for all my sanding jobs as I only use orbitals