I recently added a Tornado Tube to my Sawyer filter, so I could also connect the "clean" bottle to the filter. I haven't tested it yet, but I'm wondering if I need the syringe at all. The Platypus gravity system just backflushes by raising the clean bottle higher than the dirty bottle; could I do the same thing by inverting the unit and squeezing the clean bottle to fill the dirty bottle?

I'm going to give it a try next trip, and see what happens.