What are Cesspits and Cesspools used for?
If you live in a rural area with no access to mains drainage you may need to install a cesspit (also known as a cesspool) but this is really a last resort sewage system. Unlike a septic tank or sewage treatment plant a cesspit does not discharge waste water (above or below ground) it is just a very large holding tank that must be emptied regularly as it inevitably fills up.
When would you need to install a Cesspit?
As noted above, a cesspit is a "when all else fails" solution to waste management. However if you have carried out a percolation test as described HERE and your results are not good enough to have a soak away plus you are not near an above ground water source to facilitate discharge from a sewage treatment plant, you may have no option other than to install a cesspit or cesspool.