P-traps shall be considered self-scouring. Which statement is correct?

• A. No, P-traps are never self-scouring
• B. P-traps shall be considered self-scouring
• C. P-traps must be self-contained
• D. P-traps require separate cleaningouts

Answer: (B)

P-traps are designed so that the flow of wastewater through them tends to wash the interior surfaces, helping to flush away solids rather than letting debris settle in the bend. This flowing, scouring action comes from the trap’s curved shape and the velocity of the water as it exits into the drain, creating enough turbulence to keep the trap cleaner during normal use. Because of this behavior, they are regarded as self-scouring, which is why the correct statement affirms that P-traps shall be considered self-scouring.

The idea that P-traps are never self-scouring contradicts how their geometry interacts with flowing water, so that option isn’t accurate. The notion that they must be self-contained isn’t about their cleaning action and isn’t the defining point here. While some installations may require access or cleaningouts for maintenance, that requirement isn’t what designates a trap as self-scouring; the property comes from the trap’s ability to tend to clean itself under regular flow.