Take off the handle it can be replaced later if you want. Sit the fan on top of the bucket and place small pieces of tape all around the edge and stick it to the bucket. Then with a long piece of tape go right around making sure the connection is airtight.
Test your fan and tape any places where you can feel air escaping. Ducting is also available in a pvc type instead of the aluminium foil. You can also buy connectors to join lengths of ducting to make it longer so it can reach outside.