National Water Supply and Sanitation Council
Baseline Study
Pour-Flush Toilet Connected to a Double Pit Latrine
Level:
Next component technology options
On-site wet system
May be upgraded by connecting the liquids disposal via a small diameter sewer to a central collection sump or existing sewer system
Inspection chamber
0.15 m approx. 1 m approx. 1 m
Description:
A toilet with a water-seal arrangement: a trap fitted into the floor slab, connected to two shallow pits (side by side) by pipes. Only one pit is in use at any time. The pits are generally lined.
Principles of operation:
As for the pour-flush toilet with a single pit. An inspection chamber containing a “Y junction” is built between the pits and the pan so that excreta can be channelled into either pit. One pit is used until filled to within about half a metre of the top. When the first pit is full, the inspection chamber is opened and the stopper blocking the outlet pipe removed and placed in the other outlet pipe. The contents of the first pit are dug out after a period of at least two years, Only after this period the contents have become less harmful.
Operational and institutional requirements:
As for the pour-flush latrine, except that promotion of manual emptying by the householder is usual, and use of decomposed waste as a soil conditioner possible. Suitable disposal site necessary if the compost is not used for agricultural purposes.
Costs:
A pour-flush toilet connected to a double pit latrine costs between € 230 and € 310. Actual costs will depend on the pit volume the quality of the lining, slab and superstructure whether materials are available locally and local prices. Operation and maintenance account for around 1.5 % of the investment costs per year plus the amount for hiring local labour for emptying if this is not done by the household. Because water is required for flushing the price of water has to be taken into account.
Experience and comment:
Double pour-flush latrines are not common in Zambia. They are mainly found in countries where water is used for anal cleansing.
Experience acquired in other countries shows that resistance to handling of decomposed waste and timely changeover of pits by householders has often been overcome through education and over time. This alternative is often applicable where rocky or groundwater conditions prohibit deep excavation or reliable emptying services not existent.

A DVANTAGES
+ Does not require electricity.
+ Can be built by the household.
+ Easy to build locally with commonly available materials.
+ Once constructed the toilet is permanent.
+ Great flexibility in its application (‘offset’ pit latrine).
+ Great flexibility when planning the site layout and access (possible to locate actual toilet inside the house whilst the pits are elsewhere).
+ Only a small volume of water is needed (1 to 6 litres).
+ Once constructed the pits and the superstructure are permanent.
+ Suitable where water has to be carried to the latrine from a standpipe, well, or other water source.
+ High potential for upgrading.
+ Low construction skills needed.
+ Municipal involvement can be limited to design and maintenance guidelines.
+ Easy removal of solids from the pits as they are shallow.
+ Compost can be used as a soil conditioner after 1 year.
+ Sullage can be used for flushing.
D ISADVANTAGES
- Pits must be 15 – 30 metres away from ground and surface water sources.
- Groundwater table must be about 1.0 m below soak-away pit.
- Requires stable soil conditions and soil permeability of

10 -7 m/sec.
- Pits often fill up too quickly in soils with low infiltration and leaching capacity or if the water table reaches into the pit.
- Risk of clogging and overflow.
- In hard soils it may be impossible to dig.
- Full lining to the bottom is recommended.
- Leakage between pits occurs if the soil is too permeable.
- The “U-trap” can become blocked if it is badly designed and the toilet is not correctly used.
- Diversion boxes or PVC pipes can become blocked.
- Requires manufactured parts (water seals, toilet bowls).
- Excreta in double pits may not decompose completely, because the pit contents stay too wet.
- Not suitable for flood prone areas.
- Badly-sited latrines can get flooded or undermined.
- Cultural resistance against handling human waste may prevent households from emptying their own pit latrines, but usually local labour can be hired to do the job, but this increases O&M costs.
- User education on how to empty the pits and on how to handle and use the compost for agricultural purposes is necessary.
- Should only be used in areas with adequate water for flushing.
- Diversion boxes or PVC pipes can become blocked.
- Careful operation is essential.
- Adequate disposal site is necessary if compost is not used.
- U-trap get damaged easily if unblocking has not been done correctly (sometimes U-traps are broken on purpose to prevent blockage).
- An offset system requires more water for flushing than a direct pit system.
- Potential advantages of ecological sanitation can only be realized as long as the system functions properly.

A DVANTAGES
+ Absence of smell in latrine.
+ Control of insects.
+ Contents of pit not visible.
+ Excellent from the user’s point of view.
+ Most appropriate for people who use water for anal cleaning, and squat to defecate.
+ Valuable humus is produced.
D ISADVANTAGES
- Excreta may be visible.
- Nuisance through cockroaches.
- Does not prevent mosquitoes from breeding in the pit.
- Children may be afraid of using the latrine if the latrine is dark and the drop hole too big.
- If abandoned pit must be covered with 0.5 m of top soil to hygienically seal it off.
- Effluent may contaminate groundwater.
- Extra cost of vent pipe and proper superstructure; community may not be able to bear the higher costs.
- Effluent may contaminate groundwater.
- Sanitising and recycling human excreta is inevitably more complex than simply disposing of them as wastes.
- Extra cost for pour flush bowl.
- Full-flush pans are sometimes used when pour-flush pans are not available, but they require more water (7 to 12 litres per flush), which may be a problem if water is limited and soil permeability is not sufficient.