Plumbing in buildings: An anti-siphonage (anti-syphonage) pipe is fitted where to prevent trap seal loss by siphonage?

Introduction / Context:
Fixture traps must retain a water seal to block sewer gases. Siphonage during flushing can pull the seal away unless a vent (anti-siphonage pipe) is correctly installed. Understanding where to place this vent is central to sanitary plumbing design and codes.

Given Data / Assumptions:

• Conventional water-closet (W.C.) with a P- or S-trap.
• Risk of self-siphonage or induced siphonage during high discharge.
• Vent piping can equalize pressure across the trap.

Concept / Approach:
An anti-siphonage (vent) pipe connects near the trap arm to equalize pressure, preventing negative pressure that could suck water out of the trap. This venting is part of standard building plumbing systems and ensures hygienic conditions by maintaining the trap’s seal depth.

Step-by-Step Solution:
Identify the problem: trap seal loss due to pressure drop.Mitigation: provide a vent path to atmosphere via anti-siphonage pipe.Location: connected with the W.C. trap (or close on the trap arm) per code.

Verification / Alternative check:
Plumbing codes (e.g., IPC) require trap venting; anti-siphonage pipes or vents are connected near traps, not at manholes or main sewers.

Why Other Options Are Wrong:
Septic tank/manhole/street sewer: Venting there does not protect the individual fixture trap from local pressure fluctuations.Gully traps only: W.C. traps specifically need anti-siphonage protection.

Common Pitfalls:

• Assuming any vent in the system protects every trap; vents must be correctly located.
• Ignoring maximum trap-arm length limits which affect siphonage risk.

Final Answer:
With a W.C. trap (vent connection)