elevated location in operation tank 37b is filled with water 49 and closed to the atmosphere once tank 37b is closed to the atmosphere a flow of water 49 flows through tubes 16 and 17 creates a negative pressure within the flow system floating liquid layer 25 when of sufficient thickness will enter lower end of downcomer tube 31 through tube 34 to tank 37b displaced water from tank 37b flows back to water 61 via tube 33 exiting below the liquid surface referring to fig7 b apparatus 91 used for oil recovery from a flow system sump 61 as indicated by flow arrows is shown with fixed downcomer tube 34 positioned within floating liquid layer 25 above water 49 in sump 61 tubes 33 and 34 communicate with tank 37b at the top in operation tank 37b at an elevated location is filled with water 49 and closed to the atmosphere once tank 37b is closed to the atmosphere a flow of water 49 flows through tubes 33 and 34 creates a negative pressure within the flow system floating liquid layer 25 when of sufficient thickness will enter lower end of downcomer tube 31 flow through tube 34 to tank 37b displaced water from tank 37b flows back to water 61 via tube 33 exiting downcomer tube 31 below the liquid surface occasionally undesirable releases occur where the liquid sinks in water is not soluble in.