Abstract: A method and container assembly for storing toxic material. An original container of toxic material is positioned within a first container and is insulated therefrom by sealant material. The first container is in turn inserted into an outside container and spaced therefrom by additional sealant material. Relief valves are positioned on the containers to allow complete filling of the space between containers with sealant material. A cap is sealingly mounted to the outside container and is fixedly secured to the first container.