According to the Tygon web-page (
www.tygon.com, follow some links...) all formulations of Tygon tubing have Excellent resistance to Iodine. (One of the reasons I don't mind paying a bit more for Tygon lab-grade over ClearFlex/vinyl/etc. - it's resistant to a damn lot of stuff, I don't worry about coolant additives much)
I also wonder how the stuff you can get at outdoors equipment stores for making ground/stream/lake water safe to drink would work. I'll have to try and stop by MEC next time I'm downtown and see if I can see what chemicals are in that stuff.