Abstract: A pouring spout assembly removeably fitted inside the mouth of a supply container includes an elongate spout for pouring liquid from the supply container to the target container through a spout exit opening. This spout further includes a tubular vent extending from the interior of the supply container to a vent opening adjacent the spout exit opening. A cap is threaded on to the mouth of the supply container and provides an air tight seal between the inside of the supply container to the atmosphere. A valve is provided, which valve is resiliently biased to a normally closed position to prevent fluid flow through the spout and to prevent air from being drawn through the vent. Structure is provided so that a user may manually open the valve by the act of inserting the spout into the target container.