A cesspool combines the septic treatment tank and absorption system into a single component.

All of your household waste exits your home through a pipe that is directly connected to a cesspool. There is no septic tank involved. 

Basically a cesspool is a stone, concrete block or pre-cast concrete lined pit into which sewage is discharged. The pit is a circular hole usually drilled into the soil ; depth of the pit may vary from 5 to 25 feet.

Solids remain in the pit, effluent is absorbed into soil below and at the sides of the cesspool. Solids settle to the bottom, floating grease and scum collect at the top, and liquid seeps into the ground, initially through the bottom and most of the time through the side of the cesspool.

While cesspools have been used for a long time, since the development of the more modern septic system (tank and drain field) cesspools have often used where there is limited physical space (no room for a leach field), and perhaps where the soil absorption rate was high such as areas of gravel or sandy soils.

I most areas cesspools have been banned.

Cesspool Service:

If the waste level is within 12" of the inlet pipe near the top of a cesspool the system is at end of life and needs to be replaced. Some municipalities and experts will state other distances

While a septic company may offer to pump, partially pump out, or agitate or aerate the bottom sludge in the cesspool in an effort to extend its life, these procedures are potentially very dangerous and at best will give only temporary relief.