I found something that makes great ferret tubes!  The black plastic
drainage tubes at Lowe's or Home Depot in the plumbing section.  They are
ventilated and chew-proof and very rugged.  They are also very stiff unlike
dryer venting and completely climbable on the inside, so you can have it
even going straight up.  The best thing about them is cost, we got a 10 ft
section for about 3 bucks.  Ferret tested and approved!
[Posted in FML issue 2967]