Item 17________blank should never be allowed down a drain when a septic tank and drain field system is being used for sewage disposal.

When using a septic tank and drain field system for sewage disposal, it is crucial to understand what substances can harm the system. Specifically, Item 17 refers to fat, grease, or cooking oils. These should never be allowed down a drain because they can solidify within the tank or the drain field, leading to clogs and impairing the functioning of the septic system.

Furthermore, disposal of such substances can result in environmental contamination, as well as costly repairs. To maintain your septic tank and drain field effectively, it is advisable to dispose of fats, grease, and oils through the trash rather than pouring them down the sink. Regular maintenance and awareness of what to avoid can prolong the life of a septic system and ensure it operates efficiently.