Septic tank design detail — inlet chamber floor slope: The bottom of the sewage inlet chamber in a septic tank is provided with an outward slope of:

Introduction / Context:
Small on-site sanitation systems such as septic tanks include inlet arrangements that prevent scum carryover and promote smooth flow. The floor of the inlet chamber is given a gentle outward slope to guide influent beneath the scum layer toward the main tank volume.

Given Data / Assumptions:

• A standard septic tank with inlet chamber and baffles/tees.
• Practice aligned with common design handbooks used in building sanitation.
• Outward slope refers to the fall away from the wall toward the tank interior.

Concept / Approach:
A slope that is too steep creates unnecessary velocities and turbulence; too flat may allow deposition. Practical guidance typically specifies a modest uniform slope that reliably directs flow under the scum blanket and reduces stagnation.

Step-by-Step Solution:
Identify conventional value ranges used for inlet chamber floors.Among the listed ratios, 1 in 10 is a widely cited practical slope for septic inlet chambers.Thus select 1 in 10.

Verification / Alternative check:
Typical plumbing and public health engineering manuals show slopes around 1 in 10 for such small chambers to maintain self-cleansing at low flows without surging.

Why Other Options Are Wrong:
1 in 5: overly steep for this location; may induce turbulence.1 in 15, 1 in 20, 1 in 25: flatter than customary practice, increasing risk of local deposition.

Common Pitfalls:

• Confusing inlet chamber slope with the general sewer gradient.
• Placing the slope inward (toward the wall) rather than outward toward the tank.

Final Answer:
1 in 10