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added to decrease the viscosity and enable pumping (see Figure 2.2.). Pit latrines which are unlined or
partially lined also frequently require flushing with large amounts of water in order to pump the FS, as
liquid leaching from the pit increases the thickness of the FS. FS that has been removed by pumping is
generally more dilute and less viscous than FS that is manually collected.
Technology
FS emptied from septic tanks will be more dilute if more supernatant than sludge is collected, or if the
pump is not strong enough to remove all of the accumulated sludge. For example, in Dakar, Senegal,
83% of collection and transport vehicles are equipped with pumps and not strong vacuums, and are
therefore unable to remove solids settled at the bottom of septic tanks (Diongue, 2006; Sonko, 2008).
Where soak pits are used for the infiltration of septic tank effluent, these may also require emptying
of sludge due to clogging. Collection methods are covered in more detail in Chapter 4, Methods and
Means for Collection and Transport.
Figure 2.2
Addition of water to aid in collection of feacal sludge from a pit latrine utilising a “Gulper” in the Kibera
informal settlement, Nairobi, Kenya (photo: Linda Strande).
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