A flow set which enables the sequential administration of two liquids from a pair of containers to a patient. The flow set has a pair of valve assemblies each in communication with a container. Each valve assembly has three ports communicating through a communication chamber; an inlet port being sealed with a first one-way valve allowing flow of liquid through it only into the chamber, an outlet port being sealed with a second one-way valve allowing flow of liquid through it only out of the chamber, and a pump communication port. A pair of inlet tubing segments each connect a container to the inlet port of a valve assembly. A connecting tubing segment connects the pump communicating ports of the two valve assemblies. An outlet tubing segment connects to the outlet port of each valve assembly for delivery of the liquid to the patient. A pump is connected to the connecting tubing segment. By reversing the pumping direction of the pump, liquid may be sequentially draw from one container or the other.