I've had a few fermentations like that. I've never changed out the blowoff tube. I just secondaried one today. Luckily, I had the better bottle in a big tub with the blowoff reservoir in there as well. I put the better bottle cardboard box over the top of the carboy and that contained a nasty yeast spurt when the bung popped out (luckily I heard it pop and quickly secured it back in there with sanitized foil and a rubber band). I did have a scary moment when I was securing the bung back in there. The turbo stream of CO2 completely stopped and I thought that I had created a gap between the hose and the bun. I sprayed starsan all over the whole thing to look for bubbles, but everything seemed airtight. After about 2 minutes of puzzled staring, I heard the BB actually groan and then saw a big plug of trub sliding through the tube. After a huge hippo fart, all was well again. There was about 1/8" of yeast/sanitizer overflow in the tub and there was dried trub all over the BB, the hose, and the reservoir. The one thing I don't like about the BB is that my old big bore blowoff assembly doesn't fit (yet). Part of me thinks that theoretically, once positive pressure inside the fermenter is gone, then nasties could propagate up the blowoff tube and into the beer due to the trub lining on the tube and in the top of the fermenter. But by then the alcohol is up and the sugars are down, and I am really lazy, so I never worry about it.