To prevent backfilling with sewage, where should a toilet diaphragm pump be located in relation to the holding tank?

To effectively prevent backfilling with sewage, a toilet diaphragm pump should be installed above the top of the holding tank. This placement creates a gravitational advantage that ensures any wastewater is pumped away from the holding tank and effectively avoids any potential for sewage to flow back into the system. When the pump is located above the holding tank, the pump's operation helps maintain a continuous flow of waste material out of the tank, minimizing the risk of backpressure that could force sewage into the toilet.

In contrast, positioning the pump at the same level as the holding tank or below it could lead to issues such as inadequate drainage. If a pump is situated at the same level, it may become less effective due to the lack of gravitational force assisting the movement of waste, leading to possible backflow. Likewise, placing the pump below the holding tank could risk the pump being overwhelmed by sewage, allowing waste to potentially spill back into the toilet line due to increased pressure when the pump isn't operating.

Overall, the correct configuration for optimal sewage management and to prevent backfilling issues is to ensure the diaphragm pump is installed above the top of the holding tank.