A micro-fluidic device comprises a body. The body defines pneumatic ports, chambers for receiving liquids, and a connecting conduit. Each port is sealed with a seal and is shaped to couple to a pneumatic conduit through the seal. At least some of the chambers each have a top opening and a bottom opening. The top openings are in fluid communication with corresponding ports. The bottom openings are in fluid communication with one another through the connecting conduit, which is above the bottom openings. Selective application of pneumatic pressures to the chambers through the pneumatic conduits can transfer a liquid from one chamber to another through the connecting conduit, for example, for processing bio-samples within the device.