What is the term for the fall (pitch) of a pipe in relation to a horizontal plane?

The term for the fall (pitch) of a pipe in relation to a horizontal plane is known as "slope." This term is crucial in plumbing because it describes the angle at which a pipe is installed, typically in relation to ensuring that wastewater flows smoothly towards a drainage point or sewer. The correct slope is necessary to prevent issues like stagnation, blockages, or improper drainage, which can lead to larger plumbing problems.

In plumbing installations, the appropriate slope is generally specified (like a quarter inch per foot for waste pipes) to ensure effective drainage. A pipe that is not sloped correctly can cause backup or poor system performance. Therefore, understanding "slope" and its importance in plumbing design is fundamental for anyone learning the International Plumbing Code. Other terms like declination, angle, and elevation refer to different concepts without the specific implications related to the direction and flow of liquids in plumbing systems.