What is the name of the compartment in a septic tank that is usually extended above the surface to prevent infiltration?

The compartment in a septic tank that is commonly extended above the surface to prevent infiltration is referred to as the "leaching chamber," although the term in this case used in the answer may not precisely match typical terminology. Typically, leaching chambers are designed to allow treated effluent to disperse into the surrounding soil while preventing groundwater pollution and providing a flow of air to facilitate the aerobic breakdown of remaining contaminants.

The leaching chamber functions within the larger context of the septic system, collecting effluent from the tank and distributing it evenly into the soil. By maintaining a higher elevation, it reduces the risk of surface water infiltration, especially during periods of heavy rainfall or flooding.

In contrast, sedimentation chambers, chlorination chambers, and sewage chambers play different roles within wastewater management. Sedimentation chambers allow solids to settle out of the effluent, chlorination chambers help disinfect the effluent before it is released, and sewage chambers are often used to store raw sewage temporarily. None of these directly pertain to the issue of preventing infiltration as effectively as the leaching chamber does.