Home Inspection State Practice Exam

When a gurgling sound is heard from the tub drain after flushing the toilet, what is the most likely explanation?

1. Pipe blockage in the drain line

2. Improper venting of the plumbing system

3. Water discharging from the toilet pulling water from the tub trap

4. Defective tub drain assembly

The correct answer is: Water discharging from the toilet pulling water from the tub trap

The situation described, where a gurgling sound is heard from the tub drain after flushing the toilet, most likely indicates that water discharging from the toilet is creating a negative pressure in the plumbing system. This negative pressure can lead to a siphoning effect, which pulls water from the trap of the nearby tub drain. Traps are designed to hold a small amount of water to prevent sewer gases from entering the home, but when water is rapidly moved through the plumbing (as with a toilet flush), it can disturb this balance. In this case, as the toilet flushes, the expelled water flows through the drain pipe, creating a pressure differential. If the plumbing isn't properly vented or if there are issues such as blockages, this can enhance the gurgling sound. However, the primary cause in this scenario is the direct interaction between the flushing toilet and the adjacent tub drain's trap. Understanding this relationship in a plumbing system is crucial for diagnosing similar issues in home inspections, as it highlights the importance of maintaining a well-vented and clear drainage system to ensure proper functionality and to prevent undesirable occurrences like gurgling sounds, which indicate potential problems in plumbing performance.