Decision to make
Collect prior contracts, permits, plans, inspection reports, renovation dates, and photographs of legitimately exposed piping. Label location because supply, drain, vent, heating, and service materials can differ.
Record to build
Do not infer galvanized, copper, lead, cast iron, clay, or plastic from neighborhood, age, water color, or one fitting. Concealed transitions and partial replacements are common possibilities that require property evidence.
Question to compare
Ask the plumber to identify observed material, joining method, condition, functional symptom, inaccessible area, testing basis, repair compatibility, and why a proposed boundary is local or broader.
Useful closeout
Update the system map with verified material and location after work. Retain removed identifiers or photographs supplied safely, permit records, transition details, tests, and remaining unknown segments.