Sludge Storage Tank Manufacturer: Capability Questions That Predict Performance Sludge is the most demanding common storage duty because it attacks a tank from three directions at once: chemically from a sulphide-bearing vapour space, mechanically from grit and settled solids, and operationally through frequent cleaning. A manufacturer who has only ever built water tanks will produce a tank that passes a hydrostatic test and then, within two or three years, shows corrosion at