In a base (house) drainage system, inspection pits or chambers (small manholes) should be provided at which locations?

Introduction / Context:
Inspection pits or chambers provide access for cleaning, testing, and maintenance of house drains. Correct positioning minimizes blockages, reduces maintenance effort, and supports sanitary performance of the building drainage system.

Given Data / Assumptions:

• Pipes carry soil and waste to the intercepting chamber and public sewer.
• Chambers should allow rodding and inspection at critical points.
• Spacing and placement follow accepted public health engineering practice.

Concept / Approach:
Chambers should be installed at geometric and hydraulic discontinuities: junctions, bends (changes in direction), and gradient changes. On long straight runs, provide chambers at reasonable intervals (often about 30 m) to ensure rodding access. At the junction of a vertical soil pipe and the house drain, an inspection point is essential to control and clear blockages.

Step-by-Step Solution:
Check A: Changes in direction demand access — true.Check B: Changes in gradient can cause sedimentation or turbulence — access needed.Check C: Long straights require periodic access — around 30 m is a common benchmark.Check D: Vertical-to-horizontal junctions need an inspection point.Therefore, E (All the above) is correct.

Verification / Alternative check:
Public health manuals and codes illustrate chamber placement at each change and at set intervals along runs.

Why Other Options Are Wrong:

• Any subset omits legitimate, recommended chamber locations.

Common Pitfalls:
Omitting chambers at gradient changes; excessive spacing that prevents effective rodding; placing chambers in inaccessible locations.

Final Answer:
All the above.