An inerting and venting system for an aircraft. The inerting and venting system includes a tank containing fluid to be inerted, a mixer including an operating flow path and a mixing flow path, a vent line fluidly connecting ambient atmosphere to the operating flow path of the mixer, and an inert gas line fluidly connecting an inert gas source to the mixing flow path of the mixer. The mixing flow path and the operating flow path are arranged in a coflowing configuration such that ambient air communicated by the operating flow path mixes in a coflowing manner with inert gas communicated by the mixing flow path and the coflowed mixture is directed into the tank. The inerting and venting system may include a first valve for controlling flow of vent air from ambient atmosphere to the tank, and a second valve for controlling flow of inert gas from an inert gas source to the tank. A valve adjuster is configured to passively adjust the first and second valves in response to a pressure differential between the ambient atmosphere and the tank, and to control ratio of flow in response to oxygen concentration in the inert gas or the tank ullage gas.