Abstract: A rail tank car evacuation and transfer system and method. A method includes steps of providing an evacuation and transfer line having an inlet end and an outlet end, causing liquid contained inside the rail tank car to flow into the inlet end to at least a first location between the inlet and outlet ends of the evacuation and transfer line by pressurizing the interior of the rail tank car with a gas, sensing, at the first location, a change in the contents of the line from (a) consisting essentially of liquid to (b) including gas, and shutting off the flow through the line in response to the change.