O.K. I just got this bottle and was wondering the same thing about the stupid yellow spongy thing. I stuck it in there as is, and there is not way it will stay. Then, I pushed it down, and it just got stuck in the bottom!! So, pulling it apart totally makes sense, but I didn't want to mess it up. I do like the lens cap solution better, though. I just think I'll be splashed with no cap. I ride some pretty rough roads at times (heck, my aerobars almost fell off on one of my rides!)<br><br>
I'll try wadding the yellow thing up, and if that doesn't work I'll get the lens cap. I haven't even ridden my bike with it on yet (except on the trainer -- no bumps there!), but I don't think it is going anywhere with those rubber bands (makes it a total pain to take it off and rinse it out, though)