I had an incident today which seems to indicate that there is a flaw in how the pipe logic works. Essentially I had a jammed sewage system where my polluted water pipes backed up and refused to flow despite the fact that there was a outlet that would dump water that could not be processed into a large underground storage cavern.
As you can see the red arrows are the expected flows however you'll notice the overflow output is completely empty dispite the entire system being backed up
The issue I discovered was the fertalizer synth it seems when fluid has the potential to move in more than one direction it gets confused and the little fluid nodes go back and forth before getting stuck regardless of wether or not a valid output exists. Disconnecting the synth fixed the issue and allowed flow to resume