The pump vault must extract liquid from which zone of the septic tank?

The correct answer is the clear zone. In a septic tank, the clear zone is the layer of liquid above the scum and sludge layers, where effluent is relatively free of solids. This zone is crucial for the pump vault because it ensures that the liquid extracted is adequately treated and contains fewer contaminants that could clog the pump or disrupt the system.

When the pump operates from the clear zone, it helps to avoid drawing in larger solids which reside in the sludge zone or are floating on the surface in the scum zone. Thus, tapping into the clear zone provides a more stable and efficient effluent flow to the drain field, promoting proper septic system function and ensuring that the treated effluent is more compliant with environmental standards.