I don't say anything, just start pumping water from my cooking pot into my water bottle, using my old MSR three-stage water filter. I've done it several times before, I know what to do. The trick is to make sure they never realize that this is more for me than it is for them. I'm the one fighting nausea after all. Imagine this pot is a gorgeous Sierra lake, like Buck or Huckleberry.
Water gets through.
Now comes the lesson. Silence and intense attention. Gotta make it light, though. Students can spot pretentiousness a mile away. So, these filters are not clogged.