I think you have it about right. It clarifies that manual iso layout sketch I posted upthread.
If the wall drains were 200’ ft apart, and the underslab drains were @ 20’, then each wall drain handled 10 underslab drains. Lots of clay pipe sections with many, many joints.
You electrical types can appreciate this: each joint connection represents a potential leak and weak point.
Electrical control wiring is the same principle. You always try to make complete wire runs between terminal points to minimize splices. Each wire splice is a place where interference and static can be introduced into the system.
The electrical analogy creates visions of a Christmas tree lighting string of pigtail wire nuts (ick). Nowadays transmission line impedance integrity is critical due to the signaling rates & differential lines (RS485, etc). Believe it or not but end to end ground shifting from heavy electrical equipment switching causes more grief as this may cause the working differential voltage (in common mode) to push above or below the receiver's rated clamping limits.
IN one project, in locating the root cause failure, the micro packet protocol on RS485 signaling, would lockup in the microcontroller TX/RX circuits. It was traced back to neutral/ground reference spike shifting between floors in a building when the elevators activated. The big electrical motors caused one floor to shift differently than the other**. Nothing wrong with the control signal wiring. Can't use splicing in the impedance controlled & shielded sensitive stuff. You use impedance matching connectors (usually DB9 or better for RS485).
**Neutral/ground with reference to the central power wiring breaker box array. One solution is to use small signaling isolation transformers - but this requires a constant NRZ/NRZI type of Manchester coding (clock & data combined & PLL extracted).