David,
I've always just sketched them out myself (for residential projects). I've seen them done two ways - sanitary and supply in two separate diagrams or sanitary and supply mixed into one diagram. At the end of the day you need the hot and cold supply lines coming to the fixture and the sanitary leaving the fixture. If you're using a BIM software for your production you could model the lines in 3D and then create the diagram by turning off the walls, floors and ceilings.
Other than that I would recommend googling permit documents, or even do a public records search for permitted projects in your location. Or maybe ask a local plumbing engineer for a reference sheet to review.
Cheers.
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Jeremiah Russell, AIA, NCARB
Principal/Architect
Jeremiah S. Russell, Architect
Little Rock, Arkansas
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