A connector system is provided for use in priming a fluid circuit. The system includes a first connector and a second connector. The first connector is configured to couple with one end of a conduit. The first connector has a gas permeable membrane, a main lumen extending from the gas permeable membrane, and a second lumen. The second lumen has a first end configured to couple with a fluid source and a second end in fluid communication with the main lumen. The second connector is configured to couple with an end of a cannula. The second connector has an end configured to be inserted through the gas permeable membrane into the first connector, whereby fluid communication can be established between the main lumen of the first connector and the cannula lumen.