Which factor does NOT affect the installation of a septic system?

The installation of a septic system is influenced by several environmental and geological factors to ensure it operates effectively and safely. Availability of plumbing fixtures, while relevant to the overall plumbing system within a building, does not directly impact the septic system installation itself. The septic system's design, capacity, and efficiency depend on the site-specific conditions such as the distance to wells or drinking water sources, the slope of the land, and the soil absorption capacity.

The distance to wells or drinking water is crucial because it ensures that contaminants from the septic system do not reach potable water sources, thereby safeguarding public health. The slope of the land can affect drainage and the flow of wastewater, which is vital for the proper functioning of a septic system. Soil absorption capacity is essential for determining how well the soil can treat and absorb effluent, which directly impacts the system's design and placement.

Therefore, while plumbing fixtures are necessary for the home or building utilizing the septic system, they do not influence where or how the septic system itself is installed.