In a properly designed septic tank, where are most settable solids and scum removed?

In a properly designed septic tank, most settable solids and scum are removed in the first compartment. The design of traditional septic systems typically consists of two compartments, where the first compartment is primarily responsible for settling heavier solids to the bottom and allowing lighter materials, like scum, to float to the top.

As wastewater enters the first compartment, it experiences a reduction in velocity, which facilitates the settling of solids. While both compartments play a role in the treatment process, the first compartment is critical for the initial removal of the bulk of these materials. The second compartment further treats the effluent by providing additional time for solids to settle and for microbial action to occur, but the majority of solids and scum removal occurs in the first compartment.

This makes it clear why the first compartment is integral to the septic system's function, particularly in terms of primary treatment where the separation of solids from the liquid is crucial for preventing buildup and eventual system failure.