How is the liquid level of a septic tank determined?

The liquid level of a septic tank is determined by the invert of the outlet, which is the elevation of the bottom part of the outlet pipe that allows wastewater to flow out of the tank. This is critical because the invert level establishes the upper limit of the liquid in the tank; it essentially defines how high the liquid can rise before it spills over into the outlet.

When the wastewater fills the tank, it will rise until it reaches this level, allowing for proper drainage and functioning of the septic system. If the invert of the outlet is too low relative to the tank's dimensions or the inlet flow rate, it can lead to issues like flooding or inefficient treatment of the effluent.

Other methods such as considering the size of the tank, the volume of solids, or the inlet flow rate do not provide a direct measurement of the liquid level. The size of the tank can impact liquid capacity, but on its own does not determine the liquid level at any given time. Likewise, the volume of solids pertains to the sediment accumulation within the tank and might influence maintenance schedules, but it does not dictate the liquid level. The inlet flow rate affects how quickly the tank fills but does not establish the height of the liquid already present. Thus, the invert of