Abstract: A flexible tube check valve is introduced within a fluid path for leakage protection from flexible liquid containers. The flexible check valve can be a crossbill valve comprising multiple flexible members that restrict the flow of fluid in a tubular member. The flexible check valve is preferably functionally integrated with the container itself to prevent liquid from exiting a container. Preferably, the flexible check valve is a crossbill valve that is encapsulated within a flexible tube and mechanically attached to the flexible container. Alternatively, the check valve is manufactured as part of the flexible container. Liquid is designed to only flow through when an external compressive force (e.g. users fingers or lips) is applied to the valve. When force is no longer applied to the valve section, the valve returns to its normally closed position and fluid is wholly or substantially prevented from exiting.