A container for fluids, particularly for liquids to be subjected to extreme impact forces, for example, as created by free fall from an aircraft in flight, which container is formed from a thermoplastic synthetic resin or similarly elastic material, and including an improved filling and drain construction comprising a substantially rigid pipe section secured to an opening in the wall of the container and extending outwardly therefrom, which pipe section has a wall thickness which decreases over its length in the direction of the interior of the container, and a thinwalled tubular section secured at the opening in the wall of the container and extending inwardly for a substantial distance, two lateral edges of the tubular section being welded to flatten the thin-walled member and cause the tubular section to function as a check valve.