Side sewer, lateral, building drain, main: what do the words mean?

The route, house to street

1. Fixture drains and branches — the small pipes behind sinks, tubs and toilets, each with a trap.
2. Stack — the vertical pipe that collects the branches and vents through the roof.
3. Building drain — the lowest horizontal pipe inside the foundation, under the slab or along the basement, collecting the stacks. Usually cast iron in older houses, ABS in newer.
4. Side sewer — from the foundation wall to the public main. Seattle's word; "lateral" elsewhere. Clay, concrete, Orangeburg, or plastic depending on age.
5. Connection / tap — where the side sewer joins the main, ideally with a wye fitting.
6. Main — the public sewer in the street or alley, owned and maintained by Seattle Public Utilities (King County owns the large trunk lines).

Who owns what in Seattle

The point that surprises most owners: the side sewer under the sidewalk and street is still yours. That is why a failed connection at the main is a private repair, and why the deep street-end pit is often the expensive part of a replacement.

Terms you will see on reports and permits

• Cleanout — a capped access point for cables and cameras. Floor cleanout (inside), yard cleanout (outside near the house), property-line cleanout (near the street).
• Wye — a Y-shaped fitting that joins a branch to a run at a shallow angle so flow merges smoothly. The correct fitting for a shared-line junction and for the tap at the main.
• Saddle — a fitting strapped onto a main to make a connection without cutting it.
• Bell and spigot — the flared end and the plain end of a section of clay or concrete pipe; the joint between them is where roots enter.
• Invert / crown — the bottom and the top of the inside of the pipe. Concrete fails at the crown; cast iron fails at the invert.
• Grade / fall — the slope of the pipe, expressed as inches per foot or as a percentage.
• Right-of-way — the public strip (sidewalk, planting strip, street) between your property line and the main.
• Easement — a recorded right for a pipe to cross someone else's land, common with shared lines.
• Combined / separated — whether the main carries storm water too. See the combined sewer article.
• Backwater valve — a one-way flap that stops the main from pushing into the house.
• CIPP — cured-in-place pipe; a liner. HDPE — the fused plastic pipe used in bursting.

Why the vocabulary matters

A bid that says "replace sewer line" could mean the building drain, the side sewer on your lot, the right-of-way section, or all three. The words above are how you pin it down: from where to where, which part, whose permit. The bid comparison article uses them; so does every proposal we write.