What P-trap means
A P-trap is the curved section of drain pipe under a fixture that holds a little water, the trap seal, which blocks sewer gas from coming up the drain.
Also called trap, trap seal.
Where it matters on a plumbing job
Sewer smell from a rarely used drain usually means the trap seal dried out, which a cup of water fixes. Smell from a busy drain points to a venting or a broken trap problem. Ask which before you roll the truck.
What the model code says
- Each fixture trap holds a water seal of at least 2 inches and no more than 4 inches. (IRC 2021, Chapter 32)
- The fixture outlet can be no more than 24 inches above the trap weir and no more than 30 inches away horizontally. (IRC 2021, Chapter 32)
Check which code edition your building department enforces for P-trap before you quote.
What it costs
For P-trap, the closest koira.ai price is the drain cleaning cost guide, near $270 for a typical job and $200 to $380 for most. The guide shows its sources and what moves the price.
Work it out
- Cost guide: Drain cleaning cost
- Licensing: Plumbing license rules by state
- Tools, templates and guides: Free plumbing resources
Sources: 2021 International Residential Code, Chapter 32, Traps (ICC). Checked October 9, 2026.