Step 2: Build duct flanges from empty food cans and leftover containers!

Large empty food cans (28oz) are close enough in diameter to be re-purposed into a great adapter for standard 4" flexible dryer duct hose.  Tin snips or well-made, heavy-duty poultry shears easily cut through the can.  Combine with a standard square disposable 25oz plastic leftover / freezer container and some generous beads of hot glue to seal the deal, and for around $1 you have effectively built a dryer duct flange.  Keep the container lid handy as we will use it later as an an air-tight coupling mount on the back of the catbox.