Fluid treatment systems use disposable filters to separate chemicals, particles and odors from liquids and gases.  In the past, various structures have been used to filter liquids.  These structures include under-sink water filters having a generally cylindrical housing attached to a top manifold.  The housing accommodates a filter cartridge that should be replaced at regular intervals.  The under-sink unit is permanently mounted into the water line so that a wrench is needed to open the housing.  This makes it difficult, burdensome, and time consuming to replace the used filter cartridge with a fresh one.  Due to the labor necessary to replace the cartridges, persons would tend to change the cartridges less frequently which would limit the effectiveness of the filter. 
Quick change filter canisters and leads are disclosed by Petrucci et al in U.S. Pat.  No.  4,735,716.  The canisters and heads have cooperating tabs operable to lock and unlock the canisters on the heads in response to rotation of the canisters.  The canisters have axial necks containing both fluid inlet and outlet passages.  O-ring seals on the necks are turned with the canisters during the coupling of the canisters on the manifolds.  The O-ring seals are also directly exposed to the inlet pressure of the fluid.  The turning of O-ring seals and direct fluid pressure on the O-ring seals does not ensure an effective seal between the manifolds and filter canisters.