Runoff according to Kuitchling formula is given by,
I = 2667 / (t+20) (for storm once in 10 years)
I = 3084 / (t+20) (for storm once in 15 years)
Where t is time (minutes) and I is precipitation (mm/hr).

Water closet is of 50 mm deep, floor trap is of 50 mm deep. Various or fixtures are connected to stack through branch waste pipe of diameter 75 mm and 40 mm.

The odour threshold limit of H₂S gas is 0.008 ppm. 4 ppm causes increased eye problems.

At last main hole of building sewerage, intercepting trap is provided. It has a deep-water seal of 100 mm.

12mm chromium plated tap with appropriate marks for cold or hot water. 32 mm chromium plated brass waste coupling with rubber plug and chain. 12mm p.v.c. connector with wiped joints & 15mm chromium plated brass stop cock.

The rate of release of H₂S is high at points of high turbulence. Warm temperature conditions are required for hydrogen sulphide formation.

Vertisols (deep black clay soils) cover about 13 million ha in Ethiopia. The highland Vertisols above 1500 m altitude cover 7.6 million ha, of which 1.93 million ha are currently cropped (about 23% of all Ethiopian crop land).

Waste water is from showers, basins, kitchen sinks, washing machines and like. This is also called grey water. Normally a minimum of 75 mm diameter pipes is used for drainage of waste water.

Before development occurred most rainfall soaked into ground and contributed to groundwater recharge or was recycled into atmosphere by vegetation through evapotranspiration.

Tone ware (ceramic) pipes are used when soil and waste water is to be transported in external soil. An inspection chamber is used to clean blockage in line and change direction of pipes.