Which of the following is a primary component of a septic system?

A distribution box is indeed a primary component of a septic system. Its main role is to evenly distribute the effluent that comes from the septic tank to the various drain fields or leach fields. This distribution is crucial because it ensures that the wastewater is spread over a larger area, allowing for proper absorption and treatment by the soil.

By carefully managing the flow of effluent, the distribution box helps prevent overloading any single part of the leach field, which could lead to system failure or contamination of the groundwater.

The other options, while related to drainage and waste management, do not serve the primary function of regulating effluent flow in a septic system. For instance, a sump pump is typically used in managing groundwater or stormwater rather than household wastewater. Similarly, a composting unit is a separate waste management system often focusing on organic materials, and a stormwater drain is designed to manage surface water runoff rather than treat sewage.