In on-site sanitation using septic tanks, which of the following detailing practices are recommended for reliable operation and maintenance?

Introduction / Context:
Septic tanks are widely used for household wastewater treatment. Proper internal arrangements and clearances are essential to separate scum, sludge, and clarified effluent while preventing short-circuiting and blockage of the outlet.

Given Data / Assumptions:

• A standard two-compartment septic tank serving domestic wastewater.
• Scum accumulation at the top and sludge at the bottom are expected.
• Hydraulics should promote quiescent settling and avoid carryover of scum.

Concept / Approach:
Key geometric features include freeboard to accommodate scum swell, inlet and outlet tees or baffles to direct flow and prevent scum escape, and suitable clearances to the cover to ease ventilation and inspection. Recommended immersion of inlet and outlet inverts also stabilizes flow paths.

Step-by-Step Solution:
Freeboard: about 0.3 m provides allowance for scum and foaming.Baffles/tees: extending to scum top ensures separation and prevents direct short-circuiting.Clear space below cover: approximately 7.5 cm aids gas space and inspection.Inlet and outlet elevations: submerging inlet around 0.3 m, and setting outlet dip near 40% of liquid depth helps retain scum and draw clarified effluent.

Verification / Alternative check:
Good practice manuals and codes give similar values and arrangements that balance constructability with performance, confirming the recommendations as accepted norms.

Why Other Options Are Wrong:
Selecting only one practice ignores the others; robust septic design is a combination of features working together.

Common Pitfalls:

• Omitting inlet/outlet tees leading to scum discharge.
• Insufficient freeboard causing overflow of scum to the outlet chamber.
• Improper baffle clearances that hinder inspection or ventilation.

Final Answer:
All of the above