Leaching chambers are generally used on level lots with suitable soil conditions. Wastewater flows from the septic tank through solid pipes to one or more distribution boxes, then into open bottomed chambers that create an underground cavern that stores the waste. The wastewater floods the soil surface, prior to seeping vertically through the bottom of the trench, allowing soil bacteria and oxygen to purify it. Since no rock is used, nearly all of the soil surface at the trench bottom and side wall is exposed and available to treat the wastewater. Chambers often require less maintenance than other systems and can be installed at a shallower depth; however, due to expense of chamber units, this system may be more expensive than conventional systems.