Your best evidence may not be a fancy portfolio
For a plumber, good evidence explains the task and your contribution. Start with before-and-after job records with permitted scope, pressure checks and inspection outcome. A hiring manager needs to know whether you merely observed a project, performed an assigned step, or were responsible for diagnosing and verifying the result. Those are three very different claims.
Build three small examples
Choose one straightforward task, one unexpected problem and one quality check. Examples might center on recurring under-sink leak after repair, commercial inspection on rough-in, and drain backup requiring diagnosis rather than guesswork. For each, write the situation, what you were authorized to do, which evidence you consulted, and how completion was confirmed. Remove names, serial numbers and sensitive photographs.
Translate shop language into hiring language
Do not make recruiters decode every abbreviation. Instead of saying “helped on jobs,” say whether your work involved residential service and emergency calls or commercial rough-in and inspection work. Explain the tools, conditions and decisions that mattered. If you worked under a mentor, say so. Honest scope of responsibility is far more credible than inflated independence.
Use a skill gap as part of the story
A strong candidate can say, “I can do this under supervision, but I am still developing diagnosing the cause of a recurring leak or drainage problem instead of repeating a temporary fix.” That answer gives an employer a practical training plan. Pair your examples with a concrete next step toward moving from supervised installations to independent service diagnosis or project leadership. Do not list a certificate as a license if it is not one.
What to bring to an interview
Bring a one-page work summary, a list of equipment or environments you have actually encountered, and references who can speak to your conduct. If sharing images or documents, get permission first. The point is to make it easier for an employer to ask informed follow-up questions, not to overwhelm the interview with 40 photos.