If a tank is operating properly, solids are retained and take up increasingly more volume. At some time they must be removed. (If there is little accumulation of solids, either the household is extremely conservative with water use and waste generation or there is a problem causing solids to pass through the tank.)When there is little clear zone left, proper solids separation will no longer occur, detention time for settling is further reduced, and solids will wash out of the tank, eventually clog the soil treatment area, and cause system failure.Research on solids accumulation shows the interval between pumping depends
