It's raining here, so I decided to try it out. Of course, I was using tap water through a non-clogged filter, so I'm not 100% sure the results will play out in the field.

I attached a clean bottle of tap water (using the Tornado Tube) and the empty dirty bottle, inverted the unit, and squeezed the clean bottle. It flowed backward just fine, so I'm thinking it might work. I've got a trip in a couple weeks, so I may try it in the field then. (I'll probably take the syringe, just in case.)

Hmmm... now, in the proud tradition of gearheads, I'm finding myself compelled to overthink this: would the syringe be worth carrying anyhow, since it could be used to irrigate wounds?