A liquid/gas interface pressure accumulator and mechanical filter device is especially adapted for use within a propellant utilization monitoring system of a space launch vehicle. The device provides a retrofit solution for overcoming problems associated with liquid entering a pressure sensing lines and pressure noises that collectively harm the ability to accurately measure fuel and oxidizer levels. One device is attached to each fuel and oxidizer tank of the launch vehicle. Each device includes a housing and an internal sensing chamber that is used to accumulate liquid before it can enter a pressure sensing communication line connected to a pressure sensing transducer. The construction of the device also allows filtering of undesirable pressure noises due to vibration, pressure pulsations, and other vibratory events that occur during operation of the space vehicle. The device is also selectively tunable to filter out certain frequencies and frequency ranges/bands. The invention in other aspects includes methods of improving pressure sensing applications in a propellant utilization monitoring system.