If you don’t have access to mains drainage, then you are likely to have a cesspit or septic tank.
Septic Tank : this is essentially a mini swerage treatment plant. It works by slowing down the flow of wastes through the tank so that the solid seperates and is anaerobically digested and purified by bacteria. Usually, there are two tanks so that the solid left behind and a clearer liquid flows on. Eventually, this discharges into a disposal field where it leaches into the soil.
Cesspit : a more basic arrangement (in essence a holding tank) where solids and organic matter are retained, though liquids are allowed to pass direct into the soil.
Both tanks need to be emptied on a regular basis and careful maintenance is essential to keeping the drainage runs clear. Renewal of these systems can be expensive so getting good advice is important.