These are similar to the dry composting toilets except that they have a larger capacity and tend to stay much wetter. Their main drawbacks are the odours that are common in hot weather and, for some people, a fear of falling into them. Adequate ventilation is difficult in many versions unless assisted by fans. These types are widely used on recreation sites in North America. They have to be pumped out at intervals so that access by special truck is needed. These types can also be provided with chemicals that help to break down the excreta and mask the smells. Various proprietary versions claim to have solved the odour problem with better ventilation systems. Some can be ventilated by fans powered by solar energy or heavy-duty rechargeable batteries.
Both the types described above are suitable in locations where there is no water or power supply available. The composting type is acceptable for low usage, but only the vault will cope with a high use. The next categories depend on either a water or a power supply in order to operate.
Flush toilets with septic tank or cesspool
This type requires a consistent water supply to flush the system. This might be obtained from piped water services or by abstraction from a nearby stream, spring or lake. In many places, the water can be collected and stored in a tank or cistern to cover drought periods. The reliability of local water supplies needs careful assessment before deciding whether or not to use it.
Where piped water is available there is no such problem. Flush toilets and a water supply to basins all help hygiene and enable the toilets to be cleaned more regularly and easily. Sewage is then disposed of in a septic tank, which is either connected to a soakaway field or which yields an effluent clean enough to be discharged into a stream (as long as the relevant pollution control standards can be met). A soakaway allows the effluent to soak into the subsoil if it has good porosity (sands and gravel rather than clay) and the groundwater table is at a reasonable depth. Periodic de-sludging of the septic tank is required, but otherwise it operates to produce clean and non-polluting materials by bacterial breakdown.
Cesspools are merely means of storage in large tanks without treatment, so pumping out and transport for treatment are necessary.
The vault, pit or ‘big drop ’ toilet unit commonly used in North America. It has to be pumped out. The build-up of liquid in the vault can cause powerful smells, which the ventilation system cannot always remove.
They can smell foul, and may pollute surrounding areas if tank maintenance is not carried out properly. They are not recommended.