Materials I used:
Bathroom exhaust fan ( these fans suck air rather than blow air). Diameter 25cm (10").
Bucket or other container - the top of the bucket is slightly smaller than the fan.
Aluminium Ducting - I used 150 mm diameter x 3.6 metres (6" x 12').
The materials are best bought together to make sure that the fan just sits on top of the bucket and the bottom of the bucket is larger than the diameter of the ducting. The fan cost $30, the ducting $28, and the bucket was only a couple of dollars.