What a Plumbing Rough-In Inspection Actually Checks

At the rough-in stage, an inspector is looking at the pipe runs themselves: correct pipe sizing for the fixtures they'll serve, proper slope on drain lines so waste actually flows instead of pooling, adequate venting to prevent trap seals from being siphoned dry, and pressure or air testing to confirm there are no leaks before anything gets covered by drywall.

Venting is one of the pieces most often misunderstood by non-plumbers — every fixture trap needs an air path that lets it drain properly without gurgling or losing its water seal, and a rough-in inspection is the point where an incorrectly vented run gets caught, while it's still cheap to fix.