Container assembly including a container for storing a tissue sample and a cover adapted to engage with the container. The cover includes: a top member having a receptacle, a seal for sealing off the receptacle, a puncturing member for breaking the seal by displacement of the puncturing member. The container assembly has a first and a second position, wherein in the first position the container is isolated from the receptacle, and in the second position fluid communication is provided between the receptacle and the container. The container assembly includes a separator positioned between the seal and the bottom of the container, and the separator is provided with at least one aperture adapted to provide a fluid passage between the receptacle and the container.