This is why I always put the carboys in the tub!
The purpose of the airlock is to keep airborne bacteria and wild yeast out of the wort.
When the airlock gets contaminated with krausen, you should clean it.
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I wouldn;t say it is "contaminated" with krausen though. As long as there is positive pressure coming out of the carboy it is almost impossible for an infection to take hold. If, for instance, he has his fermenter in a "wet area" and doesn;t mind cleaning up the miess he could simply leave it until the krausen starts to drop.
Plus, (I'll say it again just to make sure everyone is listening

): if you pitch the right amount yeast (ie: that usually means making a starter with liquid yeast) at teh right temp (that means low to mid 60s for most ale strains) you won't get very many blow offs. I very, very rarely get one. If, OTOH, you pitch your yeast and leave it in your 70 degree living room with no way to reign in the temp - yeah, its probably going to go all over the place (and give you a beer with more off flavors to boot.)