A breather assembly for use with a gas turbine engine includes a static housing for accepting a fluidic mixture of substances, a rotatable separator having one or more fluid inlets and arranged about an axis of rotation, an exhaust outlet defined in the housing and positioned coaxially with the rotatable separator to accept fluidic exhaust from the rotatable separator, and a static diffuser supported by the housing at or near the exhaust outlet downstream from the rotatable separator. A portion of the static diffuser extends within the rotatable separator. The static diffuser includes a flow-straightening structure configured to reduce vortex flows in fluid flows passing through the exhaust outlet.