What materials or substances should be avoided in the drainage system to maintain safety?

The avoidance of hazardous chemicals and liquids in the drainage system is critical for maintaining safety and environmental health. Hazardous substances can include a wide range of materials such as paints, solvents, oils, and certain cleaning agents. When these materials enter the drainage system, they can pose significant risks not only to the plumbing infrastructure by causing corrosion or clogging but also to the wider environment. For instance, hazardous chemicals can contaminate water supplies and harm aquatic ecosystems if they reach water bodies. Additionally, exposure to these substances can present health risks to individuals handling the drainage system and to waste treatment personnel. Therefore, it is vital to keep such materials out of drainage systems to protect public health, the environment, and the integrity of plumbing systems.

In contrast, while food waste, paper products, and non-biodegradable items can cause clogs and maintenance issues, their impact is generally more manageable compared to hazardous chemicals. Excessive water and organic matter can lead to backup problems but are not as universally dangerous as the chemicals referenced in the correct option.