Going into the challenge I didn't have a very good idea of how exactly to make a tornado tube, but I had seen them and knew they looked pretty cool. After a fair amount of trial and error I finally figured out what I needed to do.
I used the carboy as the chamber to create and view the tornado. I used the fan assembly from the oscillating fan to provide suction to the tornado chamber. I did this by turning the fan so it sucked air out the bottom and blew air out of the top. I used the cylindrical housing from the floor fan to create a shroud around the fan assembly, directing the flow of suction into the top of the carboy.
I decided the best use of the carboy was the flip it upside down and cut out the bottom, which is now the top. I placed the fan assembly to draw air out of this hole. I used the rest of the floor fan frame to hold the carboy and fan upright. In order to give the air in the chamber the initial spin it takes to create a tornado, I drilled a row of small holes and glued in short straw parts at an angle. In retrospect the straws probably weren't necessary and the angled holes would have sufficed, but after many trials and errors I was trying anything to get it to work.
Finally, after the tornado was created I had to come up with some way to visualize it. At first I tried burning multiple incense sticks at the bottom of the carboy. But because the carboy has a slight smoky tint to it, the incense smoke was too difficult to see. I finally settled on buying a small fogger made for terrariums. You can find a cheap on on Ebay for ~$5, just search for ultrasonic fogger. Foggers like these can also be found in many newer humidifiers if you have one lying around.