Branch drains from interior clearwater inlets may not connect downstream from the base fitting of a drain stack within a distance equal to how many pipe diameters?

• A. 20
• B. 10
• C. 30
• D. 40

Answer: (A)

Connections from interior clearwater inlets to a drain stack are limited by a specific downstream distance from the stack’s base, measured in pipe diameters. The rule sets twenty pipe diameters as the cutoff: you may not tie a branch in within that distance downstream from the base fitting. This keeps enough vertical separation for proper venting and helps prevent trap siphonage or drainage issues in the connected fixtures. If a connection is needed closer than that, you’d redesign so the branch ties in upstream of the base or beyond twenty diameters. The distance is scaled by pipe size, which is why it’s expressed as pipe diameters rather than a fixed length.