The Problem
Homeowner had growing ceiling stain in living room. Two plumbers had opened the ceiling below the bathroom but found no leak.
Detection Method
Acoustic correlation from the toilet supply valve on 2nd floor to an accessible section of pipe in the crawl space. Tracer gas injected into the supply line confirmed a microscopic pinhole at a compression fitting behind the toilet — not where the plumbers had looked.
Results
Single access panel behind toilet. Fitting replaced. Ceiling repair: minimal. Total cost including detection: $1,400 vs $4,000+ in exploratory work already done.