Abstract: A stackable fluid storage tank and a sealing system for attaching to a pair of fluid containers to provide a stackable fluid storage tank. The stackable fluid storage tank includes first and second fluid containers. When the containers are mated, a first aperture on the first fluid container is in fluid communication with a second aperture on the second fluid container for providing fluid communication between the first and second fluid containers. When the containers are mated, a rigid seal tongue extending from the first fluid container is received within a seal groove defined by the second fluid container for providing a fluid-tight seal between the first and second fluid containers around the first and second apertures.