With the Katadyn Gravity BeFree 3L Water Filtration System, you no longer have to worry about where your next drink will come from. Just fill up the flask and let the gravity do the work through the EZ-Clean Membrane. Maintain the EZ-Clean Membrane quickly and easily for longer life and more enjoyment. Simply fill the flask with water, attach the cover and shake free the debris. Or, remove the filter from the flask and swish in any lake, river or stream. And when you're ready to hit the road, the collapsible flask packs small to fit into tight spaces. Just smash, stash and go!.Hydrapak Soft Flask is longer lasting, rugged, high-tech, flexible, BPA-freeNo backflushing and no clumsy tools. Simple shake or swish the EZ-Clean Membrane in the water and be on your way.