If your home is located in a rural areas you will need a septic tank and field lines because you are too far from city sewage system. The septic tank is used to get rid of solids and the field line removed liquids. Some types of soil work much better for absorbing the liquids and this should be considered when choosing a place to install the system. The property lines, drives and electric cables should also be considered when planning the correct location. The local code systems will specify how large your tank should be as well as other things that should be considered. All this is explained in detail in this video.