1)    The drains must be non-absorbent, laid on good foundations and property protected against extermal loads.


2)    The drains should be of proper size to carry the maximum discharge without flooding at any time.


3)    There should be no sharp bends or square junctions connected to the main drain, unless through chamber.


4)    The drains should be laid in straight lines and all the branch drains should be as short as possible.

5)    All the pipes, channels, bends, junctions, etc. should be of non-absorbent materials, smooth and durable.


6)    All the joints must be water-tight and vibration proof.


7)    The drains should not pass under buildings as far as possible.


8)    Inspection chambers should be provided at all changes of direction and a cleaning eye should be placed at the head of each drain.


9)    All the drains should be properly ventilated.


10) Every house drain should be disconnected from the sewer and fitted with a proper intercepting sewer trap.


11)The drains should be laid at such a level and grate that the lowest levels of a building will drain in them and will be self cleaning.


12)The internal diameter of the soil pipes, waste pipes and ventilating pipes should not be less than 75 mm and that of drain pipes should not be less than 100 mm.


13)The minimum cover of soil over the topof the house drain at the starting point should be 30 cm.


14)For maintaining self cleansing velocity (0.75 m/sec) of 0.75 m/s. A following gradients shall be adopted with pipes flowing half-full and the discharge of three times the dry weather flow.


Pipe diameter (mm)
Gradient
100
1 in 35
150
1 in 65
230
1 in 120
300
1 in 200