A cap for use in priming a medical connector that has a distal end at which is disposed a distal connection tip with an aperture through which fluid may flow, and the connector having an internal valve. The cap has a reservoir device with an internal volume and a first opening at a proximal end that is connected with the aperture of the connection tip. The reservoir has a second opening at which is disposed an hydrophobic filter for allowing gases to vent to the atmosphere while retaining liquid in the reservoir device. Over the reservoir device is mounted a slidable housing device used to activate the internal valve of the connector to a flow configuration at which fluid flows from the connector into the reservoir device. The user monitors the reservoir device and when gas has been vented so that only liquid remains, the user slides the housing device.