Ventilation system for a fuel tank comprising a pump, an active liquid/vapor separator (LVS) that can be drained using the pump, in which a roll-over valve (ROV) that is normally open brings, by default, the internal volume of the LVS into communication with the pump and only blocks this communication when the level of fuel in the valve reaches a certain height or when the tank is tilted beyond a certain angle, or even overturned.