Twin Pits for Pour Flush

The pit size depends on the number of users, but should be designed to allow for two years of accumulation, allowing the contents of the other full pit enough decomposition time to be manually evacuated.

To minimize the risk of cross-contamination, it is recommended that the twin pits be constructed 1 m apart from each other. They should also be constructed over 1 m from any structural foundation, and the full depth of the pit walls should be lined to prevent collapse and the top 30 cm should be fully mortared. These will help prevent infiltration and maintain the structure. For groundwater considerations, it is normally recommended to have a minimum horizontal distance of 30 m between a pit and a water source to limit contamination.

For the pit not in use, the idle pipe of the connecting junction should be closed or a straight pipe directly connected to the pour flush toilet.

Depending on groundwater level, the following are sample materials guidelines:

Support provided by implementer or user

Depends on pit size and number of users. However, because the pits are used alternately, pit life is virtually unlimited (one is dewatered while the other is used, then the sludge can be removed).

A physical, chemical, and microbiological analysis was conducted of pour-flush active and standing leach pits in South Africa.  The pit filling rate was estimated to be 0.11 m³/y, and fecal sludge in active leach pits had similar ash, VS, COD_T and TKN as other onsite technologies, but higher moisture content. The COD_T in pour-flush sludge decreased 85% in 27 days in a laboratory test. Microbial DNA sequencing showed both aerobic and anaerobic degradation occurred in active and standing pits.

Testing for local applicability, design, lifespan and user experience in South Africa showed successful implementation of pour flush systems over 18 months, with filling rates ranging from 114 L/yr to 392 L/yr, and easier sludge removal than VIP latrines.

Testing in rural Bangladesh indicated household acceptance, excreta decomposition for soil fertilizer, but issues with durability of the bamboo superstructure used.

An assessment was done in a settlement of the Idukki district in Kerala, India to understand the cost of open defecation and the return on investment of the twin pit pour-flush toilet. Based on the responses from 87% of the community, the rate of return was estimated as 160%.

The Twin Pit Pour Flush design is not suitable for areas with a high groundwater table or frequent flooding, or areas with clay or tightly packed soils. Health concerns include the leachate contaminating groundwater, stagnant water in pits promoting possible insect breeding, and pit failure or overflowing during floods.