Which device is NOT used to check the gradient of a drain being laid?

The circular saw is not used to check the gradient of a drain being laid. It is primarily a cutting tool designed for shaping or cutting through various materials, such as wood or metal, and does not have any capability to assess or measure angles or slopes.

In contrast, the other devices mentioned are specifically designed for leveling and measuring gradients. A laser level projects a straight line of laser light that helps ensure that the drain is laid at a precise angle, while an inclined level helps gauge the slope of the surface being worked on. Similarly, a dumpy level allows for precise horizontal leveling, which is essential when determining the correct gradient for drainage systems. Thus, these other devices serve the necessary purpose of ensuring proper drainage by checking gradients, while the circular saw does not fulfill that function.