In many parts of the world, people prefer to sit to defecate. To make a latrine seat, a support or pedestal is built or mounted on top of the slab. The seat level should be at a position that is comfortable for the majority of the users (Fig. 7.26); this is normally about 350 mm above the top of the slab.
Fig. 7.26. Latrine seat
The seat support can be made on site from brick, concrete, mud block or timber and should be designed to minimize the load on the slab. A heavy type of construction adds weight to the slab which then requires more expensive reinforcement to carry the load. Commercially available or project-manufactured pedestals made of ceramic, glass-reinforced plastic (GRP), PVC or ferrocement can also be used where people can afford them.
The inside of the pedestal should be designed to prevent constant fouling by excreta, which leads to increased odour and fly breeding. One approach is to use a large-diameter opening of 250 mm or more, but this might discourage use by children who are frightened by the large opening. An alternative is to have a 180-mm diameter hole through the pedestal which is lined with a smooth material such as cement mortar or an insert of glass fibre (Fig. 7.27) or ceramic. A third alternative is a tapered hole, increasing from an opening size of about 180 mm at seat level to 300 mm at the slab. If possible the pedestal should overhang slightly so that the seat can be used with the feet tucked under to mimic the squatting position.
Fig. 7.27. Pedestal seat liner (A)
Fig. 7.27. Pedestal seat liner (B)
Shapes of locally made pedestals vary from a rectangular box, where the user sits on one side but can also sit across a corner with one foot on either side, to a circular or oval design. It is important to obtain a good seal between the pedestal and the slab.
A seat cover may be fitted to seal off an unventilated pit. Where a vent pipe is fitted, an adequate flow of air to the pit can be obtained by raising the seat cover slightly above the seat, as is the case with conventional flush pedestals.
A special fitment with a small opening can be made to encourage children to use the latrine. Alternatively the pedestal top can be enlarged to accommodate a second seat with a smaller opening, possibly at a lower level, for the use of children.