The drainage unit is a key element to any liquid mist exhaust system. The SDU is a custom engineered weir box. It prevents air from backing up into the drainage system and allows for monitoring of oil levels. Dip tubes on the wet side of the unit trap the system and prevent oil from backing up into the drains. The dry side of the unit is designed to make flow visible through a "V-notch" weir and make the "SDU" easy to clean. All drainpipes are connected individually to the "SDU" so failure due to cross trapping cannot occur. The drain unit can be fabricated of stainless steel and is often insulated and heat traced. Carbon steel units can be coated with epoxy /urethane or other corrosion resistant finishes. Where needed, mixers and steam injectors or electric heaters can be used to keep the fluid from congealing.