A pressurized reactor system (900,1000, 1100) for bioprocessing, the pressurized reactor system comprising: a single-use container comprising a flexible wall or a semi-rigid wall including at least one of a pressure fitting and a reinforcement; a webbing or netting surrounding at least a portion of the flexible or semi-rigid wall; and at least one valve assembly (200,300) for preventing dead leg spaces in the single-use container, the valve assembly comprising: a bulkhead fitting attaching the valve assembly to the flexible or semi-rigid wall of the single-use container, the bulkhead fitting comprising an annular flange mounted on one side of the flexible or semi-rigid wall of the container such that an opening in the center of the annular flange is in communication with an aperture in the flexible or semi-rigid wall of the container; a hollow housing attached to or integral with the annular flange of the bulkhead fitting, the hollow housing comprising: a liquid inlet communicating with the opening in the center of the annular flange and configured for receiving a liquid from the container; a liquid outlet; the valve assembly including a gas port configured to be attached to a gas passageway and valve, wherein the valve is configured to selectively allow gas flow into the gas port or out of the gas port; and an inflatable and deflatable bellows or balloon fluidically connected to the gas port, and configured in a manner to inflate when gas flows into the gas port and into the inflatable bellows or balloon, thereby blocking the opening in the center of the annular flange and the aperture in the flexible or semi-rigid wall of the container, and to deflate when a vacuum is applied to the gas port, causing gas to flow out of the gas port and out of the bellows or balloon, thereby allowing liquid to flow out of the container, through the aperture in the flexible or semi-rigid wall of the container, through the hollow housing, and out of the liquid outlet of the hollow housing, the valve assembly thereby capable of preventing dead leg spaces in the container. a single-use container comprising a flexible wall or a semi-rigid wall including at least one of a pressure fitting and a reinforcement; a webbing or netting surrounding at least a portion of the flexible or semi-rigid wall; and a bulkhead fitting attaching the valve assembly to the flexible or semi-rigid wall of the single-use container, the bulkhead fitting comprising an annular flange mounted on one side of the flexible or semi-rigid wall of the container such that an opening in the center of the annular flange is in communication with an aperture in the flexible or semi-rigid wall of the container; a hollow housing attached to or integral with the annular flange of the bulkhead fitting, the hollow housing comprising: a liquid inlet communicating with the opening in the center of the annular flange and configured for receiving a liquid from the container; a liquid outlet; the valve assembly including a gas port configured to be attached to a gas passageway and valve, wherein the valve is configured to selectively allow gas flow into the gas port or out of the gas port; and an inflatable and deflatable bellows or balloon fluidically connected to the gas port, and configured in a manner to inflate when gas flows into the gas port and into the inflatable bellows or balloon, thereby blocking the opening in the center of the annular flange and the aperture in the flexible or semi-rigid wall of the container, and to deflate when a vacuum is applied to the gas port, causing gas to flow out of the gas port and out of the bellows or balloon, thereby allowing liquid to flow out of the container, through the aperture in the flexible or semi-rigid wall of the container, through the hollow housing, and out of the liquid outlet of the hollow housing, the valve assembly thereby capable of preventing dead leg spaces in the container. a liquid inlet communicating with the opening in the center of the annular flange and configured for receiving a liquid from the container; a liquid outlet; the valve assembly including a gas port configured to be attached to a gas passageway and valve, wherein the valve is configured to selectively allow gas flow into the gas port or out of the gas port; and an inflatable and deflatable bellows or balloon fluidically connected to the gas port, and configured in a manner to inflate when gas flows into the gas port and into the inflatable bellows or balloon, thereby blocking the opening in the center of the annular flange and the aperture in the flexible or semi-rigid wall of the container, and to deflate when a vacuum is applied to the gas port, causing gas to flow out of the gas port and out of the bellows or balloon, thereby allowing liquid to flow out of the container, through the aperture in the flexible or semi-rigid wall of the container, through the hollow housing, and out of the liquid outlet of the hollow housing, the valve assembly thereby capable of preventing dead leg spaces in the container.