Abstract: A container having a floor with an upper inner face and a lower outer face is provided with a drain having a tubular housing extending between the faces and a partition formed with a hole, subdividing the housing into an upper compartment and a lower compartment, and forming at the hole an upper valve seat and a lower valve seat. Respective floatable upper and lower valve bodies in the compartments sealingly engageable with the respective valve seats. Thus with this system when the upper compartment fills with liquid it floats up the upper ball to unblock the hole in the partition and let this liquid drain out. If, however, water rises in the lower compartment, it will float up the lower ball to block the passage and prevent this liquid from flowing up through the passage into the container.