Can brine from a water softener be put into a cesspit or septic tank?
A cesspit is just a storage tank that stores the sewage for a period of time and is emptied periodically by the municipality (typically every month). A cesspit does not discharge to the ground.
A septic tank is a holding tank that is intended to allow some “anaerobic” digestion of the sewage to start before overflowing to a drainage field. They are very ineffective. These are the most common private systems in the UK.
There is a third type of “on site” domestic waste treatment and this is usually referred to as “Package Treatment Plant”. These are more sophisticated in that they aerate the sewage. As you may know, we have had some suppliers of this type of equipment void their warranty if softened water is discharged - but this is for a variety of “alleged” reasons - not just salt. The issue is bigger in the US and there is a big development program investigating it with the WQA.
Increased sodium in the softened water can actually be helpful to the bacterial organisms in the septic sank.