Trying to understand the workings of the house. Where will I be able to find a plumbing diagram for my house? Does the City Hall/Planning have a copy?
In a typical residential build, the plans are not that detailed. You've probably seen movies and TV shows, where they lay out a blueprint of a building that contains all the plumbing and wiring in the building. Unfortunately, detailed plans like that, almost certainly don't exist for your home.
The blueprint for the home will show where each plumbing fixture should go, but it's up to the plumber to connect the dots. The chances of the plumber taking the time to map out where each pipe was installed, is slim to none.