Disclosed are a method and an assembly for balk transport. An inflatable bladder is inserted into a container and disposed proximal and above a gravity-fed aperture. The container may be, for instance, a hopper rail car. A bulk material then is introduced into the container, the bulk material being, for instance, a grain-based material such as corn gluten feed. The bladder is positioned and preferably secured laterally with respect to the aperture to impede access to the aperture by the bulk material. When the container has reached the transport destination, the bladder is deflated. If the bulk material has set up during transport, access to the aperture nonetheless will have been maintained.