Abstract: An enclosed storage tank for the simultaneous addition and removal, and storage, or two liquid layers of different density comprising a tank shell having a bottom, a side wall extending upwardly from the bottom, a roof supported at least in part by the side wall and at least one vertical tubular column extending upwardly from the shell bottom to at least close to the roof; a substantially horizontal first distributor plate above which the column extends and with the plate spaced above but adjacent to the shell bottom; first openings in the column between the first distributor plate and the shell bottom; a high density liquid conduit extending from outside the shell to the column interior whereby high density liquid can be fed to the column interior and then flow out the first openings into the lower portion of the tank beneath the first distributor plate and the high density liquid can be withdrawn from the tank through the first openings and then through the high density liquid conduit; a substantially horiz