A flow regulation vent for use in controlling a vent flow of washout gas in a system for supplying breathable gas pressurized to within a therapeutic pressure range above atmospheric pressure to a patient in the treatment of a sleep disordered breathing condition is disclosed. The flow regulation vent may include a housing having at least one vent orifice and at least one fixed bleed orifice; and a flap configured to regulate the vent flow of washout gas through the at least one vent orifice, wherein the at least one fixed bleed orifice is not covered by the flap in any position and the flow regulation vent provides a minimum vent flow independent of the position of the flap.