https://www.autodesk.com/autodesk-university/class/Creating-Automated-Documentation-Dynamo-2018
This is worth a watch for how the presenter automates Fire Alarm Schematics, since the core concepts are there:
- Identifying elements of interest from the model (Plumbing Fixtures)
- Converting XYZ coordinates to a 2D XY system
- Plugging in 2D symbols into a Drafting View based on the XY system, and having each symbol be based on the associated fixture type.
- Pushing parameter data from the 3D modelled fixture to the 2D symbolic fixture for annotating.
Where is stops being 'quick' is going to be the actual connected plumbing lines - you'd have to custom create the dynamo code component that would attempt to draft the mains/stacks. That can get very complex very quickly, so you may just want to stop short of this step and be satisfied with automatic symbols onto a drafting view that come with additional annotative information (fixture units, flow rates).
The complexity of the piping step is also why many firms will opt to just use isometrics for the purpose of a flow diagram - it's all modelled stuff, it's all correct, it's all already there. You just need to be willing to engage more paperspace to the task.