ANS:A - 1 in 60

The minimum gradient required for house drainage systems depends on various factors, including the type of pipes used, the size of the pipes, the velocity of flow, and the nature of the wastewater being transported. However, there are general guidelines and standards that are commonly followed in drainage system design. In typical house drainage systems, the minimum gradient or slope is usually considered to be 1 in 40 to 1 in 60. This means that for every unit of horizontal distance, the pipe should slope downward by 1 unit of vertical distance. From the options provided:

• 1 in 60 is a common minimum gradient used in house drainage systems.