Pit latrine

Digging the pit for a pit toilet in Cap-Haitien, Haiti.

A pit toilet is a dry toilet system which collects human excrement in a large container and ranges from a simple slit trench to more elaborate systems with ventilation. They are used in rural and wilderness areas as well as in much of the developing world. The waste pit, in some cases, will be large enough that the reduction in mass of the contained waste products by the ongoing process of decomposition allows the pit to be more or less permanent. In other cases, when the pit becomes too full, it may be emptied or the hole made be covered with soil and the associated structure moved or rebuilt over a new pit.

The pit toilet shares some characteristics with a composting toilet, but the latter combines the waste with sawdust, coconut coir, peat moss or similar to support aerobic processing in a more controlled manner.

Types

The slit-trench latrine is the simplest type of pit toilet, consisting of a relatively shallow (3-6 feet/1-2 metres in depth) trench narrow enough to stand with one leg on either side. This type is used either by squatting, with the users' legs straddling the pit, or by various arrangements for sitting or leaning against a support structure. Such support may vary from the simplest forms such as a log, plank, branch or similar arrangement placed at right angles to the long axis of the pit.

A cathole is a one-time use pit toilet often utilized by campers, hikers and other outdoor recreationalists.

Advanced designs

Interior of an outhouse over a pit latrine in Kouřim, Czech Republic.

A vacuum tanker for pit emptying in Chiang Mai, Thailand.

While an "advanced pit toilet" might sound like an oxymoron, in its more complex forms, or higher capacity forms - commonly associated with outhouses though sometimes used underneath a house, or as a central collection area for several outhouses or other waste collection arrangements - the pit will be larger, and covered with a supporting structure. This structure may be simply a metal plate, or board floor - with a hole over which the user positions themselves during use. A provision for seating is often placed above a pit toilet, this may be a simple hole, or several holes, in a board surface at sitting height. In bitter cold Arctic climates, honey buckets are used inside the home and carried to such covered pits outside.

A more substantial structure may also be built. Commonly known as an outhouse, these small enclosed buildings provide a roof for shelter, one or more seats with a hole in it, and occasionally access to water for washing.

Ventilated improved pit latrine (VIP)

The ventilated improved pit latrine, or VIP, is a pit toilet with a black pipe (vent pipe) fitted to the pit, and a screen (flyscreen) at the top outlet of the pipe. VIP latrines are an improvement to overcome the disadvantages of simple pit latrines, i.e. fly and mosquito nuisance and unpleasant odors. The smell is carried upwards by the chimney effect and flies are prevented from leaving the pit and spreading disease.

Odor and Insect Control Mechanism The principal mechanism of ventilation in VIP latrines is the action of wind blowing across the top of the vent pipe. The wind creates a strong circulation of air through the superstructure, down through the squat hole, across the pit and up and out of the vent pipe. Unpleasant faecal odors from the pit contents are thus sucked up and exhausted out of vent pipe, leaving the superstructure odor-free. In some cases solar-powered fans are added giving a constant outwards flow from the vent pipe.

Flies, searching for an egg-laying site are attracted by faecal odors coming from the vent pipe, but they are prevented from entering by the flyscreen at the outlet of the vent pipe. Some flies may enter into the pit via the squat hole and lay their eggs there. When new adult flies emerge they instinctively fly towards light. However, if the latrine is dark inside the only light they can see is at the top of the vent pipe. Since the vent pipe is provided with a fly screen at the top, flies will not be able to escape and eventually they will die and fall back into the pit.

To ensure that there is a flow of air through the latrine there must be adequate ventilation of the superstructure. This is usually achieved by leaving openings above and below the door, or by constructing a spiral wall without a door.

Permanent pits

A night soil man, known in his country as a frogman, manually removing the waste from a permanent concrete-lined pit toilet in Dar es Salaam, Tanzania.

Some pit toilets, which are used by a great number of people -- such as a public restroom in rural areas, or in a woodland park or busy lay-by, rest stop or other similarly busy location -- are built with a concrete lining for permanence. In this type, the pit is periodically emptied, usually by a pump mounted on a large truck which also carries a tank for storage. The waste is transported by road to a sewage treatment facility, or to be composted elsewhere. There are numerous licensed waste hauling companies providing such service in areas where it is needed.

In Dar es Salaam, Tanzania, where most human excrement is thrown into alleys or gulleys, pit latrines costing up to $300 are 10 ft (3.0 m) deep and lined with concrete slabs, while cheaper “temporary toilets” consist of a pits lined with two stacked oil drums or a stack of tires. These latrines, which are often used by several households, may be emptied by vacuum truck, manual digging, or overflowing into streets during rains.

Dry pits

This concrete-lined waste pit is one type of dry pit design. A dry pit does not penetrate the water table, while a wet pit does. In locations near streams or where undue seepage may occur, such as on a slope, the dry pit design may be preferred, even with low traffic use.

Hygienic use

Covering the deposit prevents smells and discourages some fly species which might see it as a place to feed or reproduce. Earth, sand or sawdust (six inches) can be added to simple types pit toilet after each use. Ashes and lime (one inch) are also effective.

Hazards/gas collection

Due to the possible danger caused by containing potentially explosive methane or other gases created by the decomposition of human waste, as well as to provide a more pleasant-smelling outhouse, a ventilation pipe or other arrangement is used to allow the gas to escape. In some cases, the methane may be collected for later use as fuel. see: Methane recovery (gasification)

Further reading

• Types of toilet and their suitability Practical Action