The tube is the purple round tube on this set up:
http://ecx.images-amazon.com/images/...ZL._SY355_.jpg He's always stayed in there, even though I've bought him and igloo, a little wooden house, and another bigger, better ventilated round thing that is almost just like it. [It's really an old wheel that wouldn't spin anymore and I put it in his cage.[ Also I have a small critter tail cage that I purchased believing it would be much bigger, but connected to it through tubes is a larger bin cage where I keep lots of his things. I'm just scared to remove the tube because all of his stuff is in there and I don't want him to be upset with me.