Further to Steves email about buying a cyclone lid to fit a plastic dustbin, I made my own one from information I got at this website :
http://www.jpthien.com/cy.htm It works in a similar way, but it has a baffle plate built in just below the inlet elbow so the cyclone formed is stronger and the debris drops through the slot cut in the side of the baffle also there is less chance of the debris being sucked into the outlet pipe and going to your extractor. there is also a video of it working on the website too.(the first part of video is bit boring as it only picking up the debris, but then it shows the dust extractor container empty , then shows the cyclone with all the debris in it.)
Keith.