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cerrar este libroA Guide to the Development of on-site Sanitation (WHO; 1992; 246 pages)
Ver el documentoPreface
abrir esta carpeta y ver su contenidoPart I. Foundations of sanitary practice
cerrar esta carpetaPart II. Detailed design, construction, operation and maintenance
abrir esta carpeta y ver su contenidoChapter 5. Technical factors affecting excreta disposal
cerrar esta carpetaChapter 6. Operation and maintenance of on-site sanitation
Ver el documentoPit latrines
Ver el documentoSimple pit latrines
Ver el documentoVentilated pit latrines
Ver el documentoVentilated double-pit latrines
Ver el documentoPour-flush latrines
Ver el documentoOffset pour-flush latrines
Ver el documentoDouble-pit offset pour-flush latrines
Ver el documentoRaised pit latrines
Ver el documentoBorehole latrines
Ver el documentoSeptic tanks
Ver el documentoAqua-privies
Ver el documentoDisposal of effluent from septic tanks and aqua-privies
Ver el documentoComposting latrines
Ver el documentoMultiple latrines
Ver el documentoOther latrines
abrir esta carpeta y ver su contenidoChapter 7. Components and construction of latrines
abrir esta carpeta y ver su contenidoChapter. 8 Design examples
abrir esta carpeta y ver su contenidoPart III. Planning and development of on-site sanitation projects
Ver el documentoReferences
Ver el documentoSelected further reading
Ver el documentoGlossary of terms used in this book
Ver el documentoAnnex 1. Reuse of excreta
Ver el documentoAnnex 2. Sullage
Ver el documentoAnnex 3. Reviewers
Ver el documentoSelected WHO publications of related interest
Ver el documentoBack Cover

Offset pour-flush latrines

An extension of the idea of the pour-flush pan with a water seal is for the pit to be outside the latrine building (Fig. 6.9). The contents of the pan are discharged through a short length of small-diameter pipe or covered channel with a minimum gradient of 1 in 30. PVC, concrete or clay pipes, 100 mm in diameter, are often used, but the diameter may be the same as the water seal (usually 65-85 mm). Masonry or brickwork channels with smooth circular concrete inverts have been adopted in some Asian countries. The channel is covered by precast concrete slabs or by bricks laid transversely across the top (Fig. 6.10). Pipes or channels should project at least 100 mm into the pit.

Fig. 6.9. Offset pour-flush latrine


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Fig. 6.10. Brick-covered drain


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Generally speaking, an offset pour-flush latrine requires a larger volume of flushing water than a simple pour-flush latrine. The amount of water required depends on the pan design, pipe slope and roughness. As little as 1.5 litres has been recorded as necessary for each flush, but usually considerably more than this is required.

Offset pour-flush latrines are favoured by many because the superstructure can be permanent. When the pit is full, another pit can be dug alongside and the connecting pipe excavated and relaid to the new pit without damaging the superstructure (Fig. 6.11).

Fig. 6.11. Moving the discharge pipe of an offset pour-flush latrine to a new pit


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Another benefit is that the toilet can be located inside the house and the pit outside. If this layout is used, care must be taken to allow for movement of the pipe where it passes through the house wall. This can be achieved either by cutting a slot in the wall (Fig. 6.12) so that it does not bear directly on the pipe, or by installing two short lengths of pipe (Fig. 6.13) joining in the centre of the wall. Both systems allow movement of the wall without breaking the pipe. The distance of the pit from the house wall should be not less than its depth, to prevent the load from the wall causing the pit to collapse. If this is not possible, the pit may be located not less than one metre from the wall, provided that the pit is fully lined and the unsupported plan length parallel to the wall does not exceed one metre (Fig. 6.14).

Fig. 6.12. Pipe laid through a hole in an external wall


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Fig. 6.13. Pipe fixed in place through a wall


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Fig. 6.14. Minimum distance between a pit and the external wall of a house


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