Abstract: A vertical soak tank wherein a downwardly moving compact bed of solids is contacted with liquid which floods the bed, includes mechanical components to level the solids and assure that they are maintained in a first-in first-out basis by an incoming materials distributor having inverted cones and rotating levelling rods and bars. The tank has a unique seal between a rotating bottom disc and the side walls, as well as improved means for access to the internal components. The tank also has a weighing system utilizing an external load cell to weigh the solids independently of the liquid in the tank.