Stumbled across this earlier
"Top Hat separator"
http://www.cat-vacuum-collectors.com/vacuum-hose-and-tools/hoppers.htm
Note the configuration, and the price !!!
Indeed! I wonder what it looks like underneath. I imagine there is a funnel?
(http://i66.tinypic.com/2pz9ml5.jpg) Here's the blower unit for one of those big boys. ;D