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What is a house trap?
A house trap is a U-shaped fitting on the main sewer line, usually just inside the front foundation wall of older NYC buildings, with two cleanout plugs on top. It holds water to keep sewer gas from the street out of the building, and it's one of the most common places a main line clogs.
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Where to find it
Go to the front of the basement or cellar, where the main sewer line leaves the building toward the street. Look for:
- A U-shaped section of pipe at or below floor level, sometimes in a small pit
- Two round cleanout plugs on top of the U
- A vent pipe nearby that leads to the front yard or sidewalk, the fresh-air inlet
Why house traps clog
The U-bend holds water and slows the flow. Wipes, paper towels and grease catch in the bend before they reach the street. Over time, scale and debris narrow it further.
Signs your house trap is clogged
- The basement floor drain backs up.
- Every drain in the building is slow at once.
- Sewer smell at the front of the basement.
- Water seeping around the trap plugs.
- Air or water bubbling from the fresh-air inlet outside.
What to do
- Stop water use in the building.
- Don’t open the plugs if the line is full.
- Call us for house trap and main line clearing, starting at $595 with a camera check.
Common questions
Does every NYC building have a house trap?
No, but many brownstones, rowhouses, prewar buildings and older houses do. Newer construction often doesn't.
Why are there two plugs on top?
One on each side of the U. They give access to clear the trap toward the street or back toward the building.
What is the fresh-air inlet?
A vent pipe on the building side of the trap that usually comes out near the front of the house, often with a grate or cap. If air or water comes out of it during a backup, the trap or main is likely blocked.
Should I open the plugs myself?
Not during a backup. A full line releases sewage under pressure, and old plugs are often seized. Let us relieve it safely.
Need a drain cleared?
Calls are answered 24 hours a day. A technician looks at the job and confirms your price on site before any work starts.