making interchange somewhat easier while providing minimum pressure while allowing larger and higher capacity carbon composite filters to be integrated the advantage of the tandem design is the smaller total diameter and thus the ability to fit into a substantially smaller neck bottle both designs may include a third pre filter screening element neither filter design is self venting thus it is necessary to incorporate a vent with a one way valve to permit the bottle to re inflate after taking filtered water from the bottle drinking is typically accomplished by opening the valve at the top of the bottle placing the push pull mouth piece into ones mouth and squeezing the bottle the squeezing force may be enhanced by sucking on the mouthpiece or u201c straw u201d at the same time by integrating the air relief valve into the bottle rather than the filter venting it is not necessary for the hfm to evacuate the water held within the membrane thus materially enhancing ease of use and eliminating the potential for an air blockage there is also an advantage to not incorporating the relief valve within the filter as it would be a potential point of leakage and contamination a silicon umbrella relief valve with a cracking pressure between 0 5 3 psig is mounted within a recess formed into the bottle protecting the valve from external contact this is a unique approach to maintaining the rapid flow of water without the back flushing of either filter occurring optionally the air relief valve may.