1000 Gallon Vertical Double Wall Tanks1000 Gallon Double Wall Heavy Duty Tanks are a tank within a tank providing a secondary containment solution in one unit. Environmental and safety concerns are minimal when you store your liquids in a double wall tank. Double Wall Tanks with Containment Tank Open are designed for indoor applications with stringent environmental concerns and codes. These tanks are used for the containment of chemicals, fertilizers, soaps detergents and used motor oil.