Design a VIP latrine, household of 10

Assumptions: wet pit (water used for cleaning), sludge accumulation 0.04 m³/person/year; double-pit system with each pit used for 2 years; free space above sludge 0.5 m; users = 10.

Pit size (each of two pits)

$$V = n \times r \times T = 10 \times 0.04 \times 2 = 0.8\ \text{m}^3$$

Adopt a pit 1.0 m $\times$ 1.0 m in plan: depth for sludge $= 0.8/1.0 = 0.8$ m. Add free space 0.5 m: depth $= 1.3$ m, adopt 1.5 m.

Other provisions

• Two pits of 1.0 m $\times$ 1.0 m $\times$ 1.5 m, 0.5 m apart, lined with open-jointed brick/stone masonry, top 0.3 m watertight.
• RCC slab with squat hole and foot rests; hole over the second pit sealed with a lid.
• Vent pipe: 150 mm dia (min. 110 mm) PVC pipe, 0.5 m above the roof, fly screen at top.
• Superstructure 1.0 m $\times$ 1.2 m $\times$ 2.0 m, dark inside with door facing away from the sun.
• At least 15 m from water source; pit bottom at least 1.5 m above ground-water table.

   vent pipe (150 mm, screen)
       |   ____________
       |  | superstruct |
  _____|__|____O________|__ slab
  | Pit 1 |    | Pit 2  |   1.0 x 1.0 x 1.5 m
  |  use  | 0.5 |  rest |