Which of the following is not a function of septic tanks?

The function of septic tanks is primarily to collect and treat wastewater from homes not connected to a public sewage system. They facilitate the separation of solids from liquids, allowing for the breakdown of organic matter through anaerobic bacteria, which is essential for purifying sewage to some extent, but not to the degree implied in the other choices.

Eliminating odors is not a primary function of septic tanks, as they can still produce odors if not maintained properly, especially at the surface or venting areas. The function of destroying all solid matter is exaggerated as septic systems cannot completely break down all solids; some will remain in the tank and require periodic pumping. Finally, the main purpose of septic tanks is indeed to collect wastewater, allowing for the gravitational flow into the tank where initial treatment occurs.

Thus, while septic tanks do purify sewage to a degree, their operational efficiency does not fully represent this capability as being a primary function, which is why indicating that they do not purify sewage effectively captures their limitations.