A fluid storage device for storing a first fluid in a second fluid storage container fillable with a second fluid, characterized by comprising: a first fluid storage container positionable within the second fluid storage container, the first fluid storage container being expandable and contractible between an unbiased state to a fully expanded state; a first fluid inlet coupled to the first fluid storage container, the inlet being communicable in fluid receiving communication with a first fluid source; a wall spacer positioned within the first fluid storage container that is configured to prevent collapse of the first fluid storage container; and a first fluid outlet coupled to the first fluid storage container; wherein the first fluid in the first fluid storage container is caused to drain from the first fluid outlet upon the occurrence of one or more of: the first fluid storage container filling with the first fluid to a predetermined level; the first fluid storage container having a pressure less than a pressure of the second fluid storage container; the first fluid storage container pressure achieving a predetermined threshold; the second fluid storage container pressure achieving a predetermined threshold; the second fluid storage container filling with the second fluid to apply a sufficient hydrostatic pressure on the first fluid storage container to force fluid to drain from said first fluid storage container; the first fluid outlet being opened for first fluid egress; and the first fluid storage container pressure being greater than a pressure in the first fluid outlet. a first fluid storage container positionable within the second fluid storage container, the first fluid storage container being expandable and contractible between an unbiased state to a fully expanded state; a first fluid inlet coupled to the first fluid storage container, the inlet being communicable in fluid receiving communication with a first fluid source; a wall spacer positioned within the first fluid storage container that is configured to prevent collapse of the first fluid storage container; and a first fluid outlet coupled to the first fluid storage container; wherein the first fluid in the first fluid storage container is caused to drain from the first fluid outlet upon the occurrence of one or more of: the first fluid storage container filling with the first fluid to a predetermined level; the first fluid storage container having a pressure less than a pressure of the second fluid storage container; the first fluid storage container pressure achieving a predetermined threshold; the second fluid storage container pressure achieving a predetermined threshold; the second fluid storage container filling with the second fluid to apply a sufficient hydrostatic pressure on the first fluid storage container to force fluid to drain from said first fluid storage container; the first fluid outlet being opened for first fluid egress; and the first fluid storage container pressure being greater than a pressure in the first fluid outlet. the first fluid storage container filling with the first fluid to a predetermined level; the first fluid storage container having a pressure less than a pressure of the second fluid storage container; the first fluid storage container pressure achieving a predetermined threshold; the second fluid storage container pressure achieving a predetermined threshold; the second fluid storage container filling with the second fluid to apply a sufficient hydrostatic pressure on the first fluid storage container to force fluid to drain from said first fluid storage container; the first fluid outlet being opened for first fluid egress; and the first fluid storage container pressure being greater than a pressure in the first fluid outlet.