Which of the following materials should never be disposed of in a septic system?

The correct answer—grease and chemicals—should never be disposed of in a septic system due to their detrimental effects on the system's operation and health. Grease can accumulate in the tank and pipes, leading to clogs that disrupt the flow of wastewater. This can cause backups and require costly repairs. Additionally, chemicals, whether household cleaners, solvents, or pharmaceuticals, can kill the beneficial bacteria that break down organic matter in the septic tank. The disruption to this biological process can result in untreated sewage being discharged, potentially harming groundwater and surface water.

In contrast, while food scraps, bathroom paper products, and organic waste are generally discouraged or should be minimized in septic systems, they do not pose the same level of immediate threat to the system’s function as grease and chemicals. Organic waste, for instance, can be broken down by the bacteria present in the septic tank if properly managed, while bathroom paper products are designed to dissolve. Therefore, appropriately managing what goes into the system is essential for its longevity and proper functioning, but grease and chemicals are particularly harmful and should always be avoided.