In garage floor area wastewater systems, what size submerged inlet must the drain terminate with inside the basin?

• A. 4 inch
• B. 6 inch
• C. 8 inch
• D. 10 inch

Answer: (B)

The concept being tested is how the inlet size inside a garage floor wash basin is chosen to ensure proper flow and separation within the basin. A six-inch diameter submerged inlet is specified because it provides enough cross‑sectional area to handle typical garage wash water without creating excessive velocity or turbulence. Keeping the inlet submerged below the liquid surface helps prevent odors and splashing, and it promotes settling of solids and proper oil separation before the water exits the basin. A smaller inlet would push water in too fast, risking carryover of solids and more turbulence; a larger one isn’t required by code and wouldn’t improve performance for this purpose.