Here is the link with a whole bunch of homemade ideas. It's where I found the fish tank idea. http://www.backyardchickens.com/a/homemade-chicken-egg-incubator-designs-pictures
and the one that gave me the idea. http://www.backyardchickens.com/a/homemade-incubator-2
I tried using packing tape to hold the pipe to the egg cartons. It held for most of the time. Until I added some eggs that were ready to hatch, and the chicks were getting their feet stuck to the tape, so I took it off and didnt use anything. but the pipe kept rolling around when I tried to turn the eggs.
Here are some pics of mine. I also took out the cardboard by the light. It was in my way when turning the eggs. I just put the water in the bottom of the tank. no need for a dish. The Humidity stayed at 50% and temp stayed at 100. Any adjustments I made were by adjusting the towel. The tank cover I have is screen on one half and a liftable lid on the other half. If you have any questions about wiring or anything, just PM me.
These are some great ideas----I have old tanks and never thought of doing this.
Thanks for posting