If n is the rugosity coefficient, r is the hydraulic depth, s is the bed slope of sewer, the velocity of flow in m/sec may be obtained by the formula $${\text{V}} = \frac{1}{{\text{n}}}{{\text{r}}^{\frac{2}{3}}}{{\text{s}}^{\frac{1}{2}}}$$   evolved by

The effluent of a septic tank is

A. Fit for discharge into any open drain

B. Foul and contains dissolved and suspended solids

C. As good as that from a complete treatment

D. None of these

5 days-biochemical oxygen demand (BOD5) is taken at a temperature of

A. 0°C

B. 15°C

C. 20°C

D. 25°C

The bottom of the sewage inlet chamber of septic tanks, is provided an outward slope

A. 1 in 5

B. 1 in 10

C. 1 in 15

D. 1 in 20

Drop manholes are the manholes

A. Without entry ladders

B. Without manhole covers

C. With depths more than 3.5 m

D. Having drains at different levels