Question

Which drainage trap has a horizontal outlet?

• A. P trap
• B. Nahni trap
• C. S trap
• D. Bottle trap

Hint:

Associate the letter shape directly with the pipe exit direction:
• P-trap $\rightarrow$ Horizontal exit (goes through the wall).
• S-trap $\rightarrow$ Vertical exit (goes through the floor).

Answer 1

The Correct Option is A

Concept: Plumbing traps are classified primarily by their geometric profiles and the direction of their discharge outlets. Traps are built to maintain a permanent water seal that prevents sewer gases from entering internal rooms while facilitating waste disposal.

Step 1: Structural analysis of the P-trap configuration.
The P-trap is named after its physical resemblance to the English letter 'P' when installed horizontally:
• It consists of a vertical inlet section that receives wastewater from a fixture (such as a sink or washbasin).
• The pipe then loops downward to form a water seal before bending forward into a clean horizontal discharge outlet.
• This horizontal arrangement allows the waste line to pass directly through an adjacent vertical wall behind the plumbing fixture, making it ideal for multi-story buildings with wall-hung fixtures.

Step 2: Comparing structural designs of other standard traps.
Let us examine the structural geometry of the alternative options to confirm their discharge directions:
• S trap: Shaped like the English letter 'S'. It features a vertical inlet and a downward-curving loop that ends in a vertical discharge outlet, which routes wastewater straight down through the structural floor slab.
• Nahni trap: Also known as a floor trap, this unit features a cast-iron or plastic basin with a removable grating installed directly in bathroom floors. It typically uses a gently sloped or custom-angled discharge outlet rather than a true axial horizontal pipe run.
• Bottle trap: Features a cylindrical vessel that creates a water seal within a concentric container. While its outlet pipe exits horizontally, the trap is categorized primarily as a specialized decorative or compact vessel unit rather than a basic running pipe profile like the P-trap. Thus, the P-trap is the standard configuration defined by a true horizontal outlet.