A septic tank installation can be completed with either a standard spherical tank or the shallow dig cylindrical version, where below ground space is limited. A septic tank outlet must have a soakaway, land drainage pipe system installed directly after the outlet to be truly effective. The original way to collect and treat raw sewage is a septic tank and although they are not as efficient as sewage treatment plants, these tanks represent a very competitive and effective way of dealing with sewage where a mains drainage system is not present.