User Review: Platypus GravityWorks Filter System
This filtering system is the best I've used. I am an ultralight backpacker, and I've carried and used this filter in all four seasons. It is uncomplicated and filters a lot of water very fast with no work our your part...fill it and hang it.
If you cannot find anything to hang it from, the ClearStream filters fast enough that you can just hold it up until the water moves from the "Dirty" side to the "Clean" side.
The only drawback I've found is that the "ziplock" style closures are a bit tough to seal and even more so in cold weather. However, once you get them zipped tight the water does not leak out. I love this filter.