A removable water trap device (110) removes moisture from a respiratory gas stream from a patient interface assembly (140), enabling monitoring of gas within the respiratory gas stream by an analysis bench (120). The device includes a housing (111), an upstream water trap connector (115), and a filter assembly (360). The housing includes a first portion (210) insertably attachable to a tether assembly receptacle (132) to connect the device to the analysis bench for delivering the gas stream via a tether line (136). The upstream water trap connector is attachable to a downstream patient interface connector (141, 143) in a sample flow line (145, 148) of the patent interface assembly for receiving the gas stream via the sample flow line. The filter assembly is insertably contained within the housing and configured to remove moisture from the gas stream, the filter assembly including a downstream water trap connector (116) attachable with the tether line within the tether assembly receptacle. The filter assembly is replaceable in dependently of replacement of the patient interface assembly.
