I keep all my plastics in a large pail with about 2 gallons of mild bleach solution in it. Any airlocks, stoppers, funnels, or anything else that that might be contaminated gets tossed in it and left to soak until needed.
For anything left in a bleach solution, you need to rinse 2 or 3 times in hot water to get rid of any chlorine.
I store my blow-off tube in this same pail, in the bleach solution. My tube is about 15 years old, I use it on almost every brew. I would guess that somewhere between 50 to 100 beers have had a blow-off (I like to fill the fermenter as high as I think I can), and have never had a problem.