A medical liquid transfer system includes a pump configured to transfer liquid between at least two containers. A detachable connector is detachably secured to the pump. The detachable connector has at least one pump passage to transmit pumping pressure from the pump to at least one of the containers. The detachable connector can include one or more liquid impermeable and gas permeable membranes to ensure the liquid is retained in the detachable connector. After the fluid is transferred the detachable connector is removed and replaced by a new one in order to prevent contamination of the pump. An interlock mechanism is used to prevent premature removal of the detachable connector and/or the container being filled.