When to call a plumber

• Your city requires a licensed plumber for new drains and vents, or does not issue homeowner permits.
• Tying into cast iron, or into a main stack you cannot see the bottom of. Cutting a loaded cast iron stack without support can drop it.
• Breaking a slab near the main building drain, or where you do not know the drain's depth.
• A sewage ejector on its first install: the basin, the check valve, the vent and the electrical all have to be right together.
• Anything with gas: gas water heaters, gas lines in the same wall.
• The sewer line outside the house.
• A failed inspection you do not understand. One visit from a plumber costs less than opening a wall twice.

A rough-in sheet is still useful with a plumber: it gives you a fixed scope to get quotes against.