All household waste materials flow into the tank and bacteria begins to 'feast' on the new product.  The solids sink to the bottom and the grey water 'affluent' rises and eventually overflows into a large bed of underground rocks and sand called the absorption area.  Over time, the affluent seeps through the sand, slowing filtering it.  By the time the water reaches the end of the bed, it moves through a quick chlorination filter and re-enters the water table or becomes run-off.  Solid waste should never enter the absorption area and should be avoided at all costs. It is the overflow that clogs the soil's pores and causes septic systems to fail. Two main factors cause solid material to build up enough to cause an overflow: bacterial deficiency and lack of sludge removal.