Operator terms · Wastewater
What is a gravity sewer?
A gravity sewer is a sewer pipe laid on a downward slope so wastewater flows through it by gravity alone, without pumping. Most of a collection system is gravity sewer; lift stations are used only where the ground will not let gravity carry the flow.
Last reviewed 2026-08-03
Why slope matters
The pipe is laid at a steady downhill grade so wastewater keeps moving fast enough to carry solids without settling. Too flat and solids settle; too steep and the water outruns the solids. The right slope keeps the line self-cleaning.
When pumping is needed
Where the ground rises or a line gets too deep, gravity cannot carry the flow further. A lift station collects the wastewater and pumps it up to a point where a new gravity sewer can take over.
Common questions
- Does a gravity sewer use pumps?
- No; it relies on slope so wastewater flows by gravity.
- Why does slope matter?
- The right grade keeps flow fast enough to carry solids without settling.
- What happens where gravity cannot carry flow?
- A lift station pumps it up to a new gravity line.