Noticed today when I was cleaning my air filter there was some water on the bottom of the air box, presume that the plug on the bottom of the box would release the water with gravity but to my astonisment, it doesn't unless you physically remove the plug which is totally a bad design especially if you're on the trail and going thru water/mud puddles like I did. My old bike had a plug that would let the water out but not in, basically like a check valve so beware if you're riding in deep water or mud. Guess that I need to look for a better system
If I'm riding and it's a really wet and rainy day I'll leave the plug out so it just drains on i's own. If I'm going through deep water I'll put it in. I always wear a backpack, but if you didn't want to fool with it you could always just drop it in the airbox.