The basic function of a septic tank is to separate liquids and solids. When you use the sink, flush the toilet or put something down the kitchen drain, both solids and liquids will go down at the same time. On reaching the septic tank/well, the solids and liquids will begin to separate from each other. The solids will either float to the top or sink to the bottom and the liquids will remain at the center of the well. From here, the liquids will leach and the remaining solids will gradually decompose with the help of naturally occurring bacteria.