Three ways of providing cheaper concrete slabs for large pits are domed slabs, corbelling and enlarged excavation below the topsoil. Domed slabs, as developed in Mozambique, need no steel reinforcement. They are thinner, lighter and cheaper than normal RC slabs and can be made by relatively unskilled people. Corbelling with blocks, bricks or rock is suitable for linings that are circular in plan. Overcoming smell, flies and disease Many users of crude pit latrines complain about bad odours and fly nuisance.
Flies feeding on faeces are responsible for much transmission of disease.
Flies, smells and health hazards are also, of course, major reasons for replacing indiscriminate defecation and dry latrines, and are associated with unsanitary emptying of full pits. Three methods are commonly used for preventing nuisance from flies and smells in pit latrines. These are water seals between pits and latrine shelters, using tight-fitting lids and ventilating the pit in VIP latrines. Water seals are the most effective of the three and are the first choice wherever water is used for anal cleaning and sufficient water for flushing is available. Lowest in initial cost is a slab and trap over a single pit.