---
title: "Sewer appurtenances and their necessity"
subject: "Sanitary Engineering"
chapter: 4
key: "semester_6/sanitary_engineering:sewer-appurtenances-necessity"
source: https://www.bctengineer.com/q/semester_6/sanitary_engineering/sewer-appurtenances-necessity
site: BCT Engineering
---

# Sewer appurtenances and their necessity

Sanitary Engineering · Chapter 4: Sewer Appurtenances

- Asked in: 2078 Chaitra, 4 marks; 2069 Bhadra, 4 marks (asked 2 times)
- Video: [Sewer Appurtenances](https://www.youtube.com/watch?v=w3b62C8EAVY) — Ketan Lakhtaria
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/sanitary_engineering/sewer-appurtenances-necessity
- Whole chapter: https://www.bctengineer.com/md/semester_6/sanitary_engineering/chapter-4

## Question

Define sewer appurtenances. Justify (explain briefly) the need of installation of sewer appurtenances with suitable examples.

## Short answer

Sewer appurtenances are accessory structures (manholes, inlets, catch basins) along sewers for access, cleaning, ventilation, and maintenance. They are needed to inspect and remove blockages, admit storm water, trap grit and grease, change direction, and release explosive gases.

## Answer

#### Definition
**Sewer appurtenances** are the structures and accessories built along a sewerage system, apart from the sewer pipes themselves, that help it work properly and make it easy to inspect, clean, ventilate and maintain.

#### Need (necessity) of sewer appurtenances
Sewers are underground, closed conduits. Without appurtenances it would be impossible to operate them safely. They are needed:
1. **To inspect and clean** the sewers and remove blockages.
2. **To admit storm water and surface runoff** (street inlets) in combined and storm systems.
3. **To change direction, gradient or size** of sewers and join several sewers (manholes).
4. **To reduce velocity and deliver at the lower level** on steep grounds (drop manholes).
5. **To keep the sewer self-cleansing** in flat areas through flushing devices.
6. **To keep out harmful materials**: catch basins retain grit and silt, and grease traps retain oil and grease which would block sewers.
7. **To ventilate the sewers** and prevent accumulation of explosive and poisonous gases (ventilating shafts).
8. **To cross obstacles** such as rivers and depressions (inverted siphons).
9. **To discharge sewage safely** to the receiving water (outfalls/outlets).

#### Examples and their function
| Appurtenance | Use |
|---|---|
| Manhole | Access for inspection, cleaning, junctions |
| Lamphole | Inspection of small sewers by lamp and mirror |
| Drop manhole | Brings sewage down to a deep sewer without scouring |
| Street inlet | Admits storm water from road to sewer |
| Catch basin | Traps silt, sand and floating matter |
| Flushing tank | Flushes the sewer in flat reaches |
| Grease and oil trap | Holds back oil and grease |
| Inverted siphon | Takes sewer under a stream, road or depression |
| Ventilating shaft | Releases sewer gases |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What are sewer appurtenances?
   A. The sewer pipes themselves
   B. Only the treatment plant units
   C. Structures and accessories along a sewerage system, other than the sewer pipes, that help inspection, cleaning, ventilation and maintenance
   D. Only house connections
   Answer: C. They are accessories apart from the pipes that make the system work. (Key point: Definition)

2. Which appurtenance is used to keep sewers self-cleansing in flat areas?
   A. Catch basin
   B. Inverted siphon
   C. Street inlet
   D. Flushing tank
   Answer: D. Flushing devices supply water to flush flat reaches. (Key point: Matching)

3. Which appurtenance lets a sewer cross a stream or depression?
   A. Inverted siphon
   B. Lamphole
   C. Grease trap
   D. Ventilating shaft
   Answer: A. An inverted siphon passes the sewer below obstructions. (Key point: Matching)

4. Which appurtenance keeps oil and grease out of sewers?
   A. Manhole
   B. Grease and oil trap
   C. Drop manhole
   D. Street inlet
   Answer: B. Grease traps retain oil and grease that would block sewers. (Key point: Matching)

## Related in Sanitary Engineering

- [Working of two sewer appurtenances](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Atwo-sewer-appurtenances-sketch) — Sanitary Engineering, chapter 4
- [Manhole: necessity and construction](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Amanhole-necessity-construction) — Sanitary Engineering, chapter 4, asked 3×
- [Drop manhole: need and construction](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Adrop-manhole-purpose-sketch) — Sanitary Engineering, chapter 4, asked 4×

## Related in other subjects

- [Necessity and aspects of project appraisal](https://www.bctengineer.com/question.md?key=semester_7%2Fproject_engineering%3Awhy-appraisal-necessary-aspects) — Project Engineering, chapter 2, asked 4×