A de-sanding tank with a vertical exterior wall and an interior conical bottom with a solids outlet located at a lower tip of the conical bottom. Downwardly and tangentially oriented water jet nozzles within the tank cause a swirling action to remove solids. An enclosing space located between the vertical wall and the conical bottom has a honey-combed structure of closed pore foam as reinforcement for the conical bottom. Compartments within the honey-combed structure fill with water as the vessel is placed in service to add support for the conical bottom. Water enters the compartments via downwardly facing bottom openings that fill a common void located at the bottom of the enclosing space and then into the compartments. Weep holes provided between the top of each compartment and the interior of the tank allow the air from the compartments to enter the tank as the compartments fill.