In line filters for when arriving at camp. Set it up then set camp up. Frontier, Amigo, can't recall which one no longer isn't available. I bought one and will try to rig up later, if ever. There was a thread a year ago or so on how to rig up a do-it-yourself bag. I hardly use a filter anymore here in the Sierra. When I do, I have a First Need and an original Pur Hiker when they first came out, but I haven't used it in years because the First Need water takes so much better.