TL;DR
The trap arm is the horizontal stretch of drain pipe running from a fixture trap's outlet to the fitting where its vent connects, the section whose length and slope protect the water seal in the trap. Codes cap its length by diameter, roughly five feet for 1-1/2 inch and six to eight feet for 2 inch depending on the code, because an overlong arm lets the falling slug of water siphon the trap dry.
What it means
The trap arm is the horizontal stretch of drain pipe running from a fixture trap's outlet to the fitting where its vent connects, the section whose length and slope protect the water seal in the trap. Codes cap its length by diameter, roughly five feet for 1-1/2 inch and six to eight feet for 2 inch depending on the code, because an overlong arm lets the falling slug of water siphon the trap dry. Gurgling drains and sewer odor after flushing are the classic field signs that this geometry is wrong.
Where it sits in the glossary
Trap arm is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
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