Slow, undisturbed flow through the tank is necessary for the separation
of solids and liquids and for bacterial action. Submerged inlets
and outlets or baffle boards reduce disturbance. A submerged outlet
prevents scum from passing out with the effluent.
The single-chamber tank without a siphon, shown in figure 4, is easy
to build, inexpensive, and entirely satisfactory in most instances. In
very tight soils or for large installations a siphon and sometimes two
chambers are advisable.