Hi Jay,

One disctinction to note, the shop vac filters BEFORE the airflow
reaches the impellers. This means it's better suited for general
cleanup where you might be sucking up rocks, nails, wood or metal
scraps, etc. Dust collectors generally filter AFTER the impeller
which means any debris you pick up could hit the impeller and damage
it.

What you need is one of these:
http://www.rockler.com/product.cfm?page=1515
It is a centrifugal separator that mounts in the place of the lid of a
garbage can.

Yeah, I've considered buying one of those, especially since large planer
shavings often clog up the grate on the port of my dust collector. But, I'm
already tight on space in my garage and that would complicate the mobility
of my collector. In my two-car garage/shop, everything is on wheels to
bring it out when I need it, and roll it away when I'm done.

Anthony