What building drain means
The building drain is the lowest drain pipe inside the house, collecting everything from the other drains and carrying it out to the building sewer.
Also called house drain, main drain.
Where it matters on a plumbing job
Main line clogs and backups at the lowest drain point to the building drain or the sewer beyond it. Camera it before quoting, so the price matches what is actually down there.
What the model code says
- The code defines the building drain as the lowest piping that collects drainage inside the house and extends 30 inches beyond the exterior walls to the building sewer. (IRC 2021, Chapter 2)
Check which code edition your building department enforces for building drain before you quote.
What it costs
The drain cleaning cost guide has the typical job at $270 and the usual range at $200 to $380. 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 2, Definitions (ICC). Checked October 9, 2026.