HYDRAPAK - BOTTLE Filter Cap (42mm)On the go water filtration Filter water on the go. The new 42mm Filter Cap threads seamlessly onto all sizes of HydraPak's 42mm threaded Seeker water storage bags and Flux flexible bottles morphing them into filtration solutions. The end result being lightweight filtration kits that can either be used to squeeze filtered potable water into other camp bottles and containers or to drink freshly filtered water from a Seeker, Flux, UltraFlask or SkyFlask.