How to Screen Plumbers: 9 Questions and What to Listen For Screening Interview Template

What is your current plumbing license tier (apprentice, journeyman, master), who issued it and in which state or city, what is the license number, how many documented hours do you have toward the next tier, and can you pull a permit under it?

What this assesses: License tier is the only answer here that changes what a candidate is legally allowed to do on your jobs, so score it first and verify it separately. Know how the tiers work before you read the responses, because hiring managers get this wrong as often as candidates do. Apprentice means supervised work and logged hours toward the next tier. Journeyman generally means working unsupervised on installation and service. Master is usually the tier that can pull permits or qualify a contractor license, and in most states one master has to stand behind every permit the company pulls, which is why a shop with no master in it stalls on anything inspected. The part people assume wrong is that any of this is national. Plumbing is licensed state by state, a handful of states leave it to individual cities and counties instead, and reciprocity where it exists is partial and normally means an application and sometimes an exam rather than an automatic transfer. A journeyman card from the next state over is a starting point, not a qualification. Strong answers give the tier, name the issuing authority, produce a license number without being pushed, put a real hour count against the next tier, and answer the permit question with a yes or a no. Be cautious with a candidate who says "licensed" with no tier or state attached, who cannot name the board that issued it, whose number does not match the tier they claimed, or who assumes the card travels. None of this is a judgment call you should make from the answer alone. Most states publish a free license lookup, it takes a minute, and you should run it on every candidate rather than only the ones who sound uncertain.

Is your background mostly service and repair, new construction, or remodel, and residential or commercial? Walk me through a typical day in your last role: how many calls did you run, or what did you rough in and on what schedule? Were you solo in a truck or on a crew, and who handled the customer and the price?

What this assesses: Service and new construction share a license and almost nothing else, and mismatching them is the most common reason a technically strong plumber washes out in the first month. Service is diagnosis, a stranger's house, and a price quoted at the kitchen table, six to ten calls on a normal day and more during a freeze. New construction is layout, print reading, production pace, and an inspector, measured in units roughed or fixtures set rather than calls closed. Remodel is its own thing again, mostly working around what someone else built forty years ago and whatever the walls turn out to contain. Commercial adds scale, coordination with other trades, and grease interceptors, backflow assemblies, and roof drains that rarely show up in a house. Strong answers pick a side without being asked to, put real numbers on the day, and name the part they are weaker at. A plumber who says they ran eight calls a day, kept a stocked truck, and quoted their own work is describing a very different hire than one who says they never touched a price. Be cautious with a candidate who claims equal strength across all of it, which almost always means thin exposure to each, and with anyone who cannot attach a number to their own day. Then calibrate against your work rather than against the resume. A strong new-construction plumber dropped into a service truck will be slow and uncomfortable for a quarter, and a service plumber on a commercial rough will move fast and be out of their depth at the inspection. Either can work if you know which one you hired and you plan the ramp. The failure is finding out in week three.

A homeowner calls: every drain in the house is slow, the toilet gurgles when the washing machine drains, and there is water standing around the basement floor drain. Walk me through what you check, in order. At what point would you run a camera, what would you quote, and what would you tell the homeowner?

What this assesses: This separates a plumber from a drain cleaner, and the order of the answer is the whole grade. Several fixtures slow at once, a gurgle when a high-volume fixture drains, and water at the lowest drain in the house all point the same direction, which is a blockage in the main line downstream of everything rather than a problem at any fixture. Strong answers say that within a sentence or two and head for the main cleanout instead of pulling a P-trap. From there the sequence matters: find and open the cleanout, note whether it is standing full and how fast it drains back, clear it with a cable or a jetter depending on what they expect to find, then run a camera before calling it finished. The camera is the line between a repeat call and a repair. Roots at a joint, a belly holding water, an offset at a settled section, a collapsed clay tile, and forty feet of wipes and grease all clear the same way and mean completely different quotes. The best answers also locate and mark depth on any defect they find, because that is the difference between quoting a spot repair, a liner, or a full replacement and guessing at one. On the homeowner half, listen for showing the footage rather than describing it, and for an honest split between the price to open the line tonight and the repair conversation tomorrow. Be cautious with anyone who starts at a fixture, anyone who cables and leaves without looking, and anyone who quotes a dig before they have located anything. Be cautious too with a candidate whose entire answer is which machine they would bring, because the tool is not the diagnosis.

What have you worked with, and where would you want support: PEX and by which joining method, copper by solder or press, cast iron, PVC and ABS, galvanized, gas piping including CSST, tank and tankless water heaters, backflow assemblies, sewer camera, locator, and jetter? What do you run start to finish on your own, and what do you hand off?

What this assesses: The handoff half is the useful half. Every resume lists every material, and the plumber who can say exactly where their line sits is almost always the one who can work up to it. Strong answers read like an inventory rather than a claim. They name joining methods instead of materials, which is where the real experience lives: expansion, crimp ring, cinch clamp, or push-fit on PEX, and solder versus press on copper, which matters more than it used to now that press is standard on much commercial work and a plumber who has never run the tool will be slow on your first job. They know cast iron means a snap cutter, no-hub bands, and supporting the pipe before you cut rather than after. They are specific about gas, which many states license or endorse separately, and a candidate who mentions that CSST has to be bonded has read the code rather than the instructions. Backflow is the clearest escalation signal on the list, because testing an assembly takes its own certification and a test kit with current calibration, so a plumber who says they install them but do not test them is giving you an honest and correct answer. Medical gas is the same story under ASSE 6010 if you touch healthcare work. Be cautious with a candidate who claims every system and every brand at one level, since that is rarely true and shows up later as callbacks. Be equally cautious in the other direction if the handoff list runs long enough that you are paying journeyman wages for a helper. Then weight all of it against your actual job mix. If most of your revenue is tankless service or commercial backflow, the sentence about that one system outranks everything else in the answer.

Tell me about a time an inspector failed your work, or a job you finished that came back as a callback. What specifically was wrong, what did the correction cost in hours or dollars, and what do you do differently now?

What this assesses: Every plumber who has worked long enough has failed an inspection, so a denial here is a larger flag than an admission. What you want is the specific code item, named correctly. The common ones are worth knowing so you can tell a real story from a manufactured one: an S-trap where a vented P-trap was required, an air admittance valve used where the jurisdiction does not allow one, not enough fall on a drain line, which on small-diameter pipe is generally a quarter inch per foot, a missing or buried cleanout, no thermal expansion tank on a system closed off by a backflow preventer or a check valve, a TPR discharge line terminating somewhere it should not, support spaced too far apart, or copper landed straight onto galvanized with no dielectric between them. Strong answers name the item, describe the correction, put a rough cost on the rework, and say what changed in their routine afterward, which is usually a checklist or a habit of calling for rough inspection earlier. The best answers include the unglamorous version, a callback on their own work that no inspector ever saw, because that is the one nobody has to admit to. Be cautious with a candidate who says it has never happened in fifteen years, with one who blames the inspector without ever stating what the code required, and with one whose only example is somebody else's mistake that they happened to find. Be cautious too with a plumber who treats a failed inspection as a paperwork problem rather than something they built wrong, because that is the person who will argue with your inspector on your permit.

Most of this work happens in someone's home, and in service the price comes up before the repair does. Walk me through how you explain a repair and its cost to a homeowner who is upset about the number. Then tell me about a time a customer declined the work you recommended, and what you did.

What this assesses: In service plumbing the conversation at the kitchen table drives both the ticket and the review score, and this skill is uneven even among excellent technicians. Strong answers describe a routine: explain the failure in plain language without trade shorthand, show the homeowner what they found rather than telling them about it, give options at more than one price when honest options exist, separate what is urgent tonight from what can wait until spring, and put the number in writing before touching anything. The declined repair is the real test. Good answers document what was recommended and what the customer refused, leave the house on decent terms because that customer calls back the next time the line backs up, and do not treat a decline as a failure. Be cautious with a plumber who is dismissive of homeowners as a group, who describes the whole conversation in closing language, or whose response to an upset customer is to drop the price on the spot, since that technician will discount your margin away every time someone frowns. Be cautious in the other direction with hard-sell instincts, particularly any version of scaring a homeowner into a repipe. Those produce one good week and a permanent review. If the candidate has never quoted a price at all, that is not disqualifying, it is a new-construction background, and it tells you to pair them with someone for a month rather than handing them a truck. Decide which failure your company can absorb before you score this one, because a shop billing flat rate and a shop billing time and materials are hiring for two different answers.

It is 9 p.m. on a Saturday. A homeowner calls: sewage is coming up through the basement floor drain and the shower, there are two small children in the house, and it is still rising. Walk me through your first fifteen minutes. Separately, what changes if the after-hours call is a gas smell inside the house?

What this assesses: Sequence is the entire grade on the first half, and this is where written answers beat a phone screen, because you can lay six candidates' first fifteen minutes side by side. Strong answers stop the water going in before anything else, which means telling the household to stop flushing, stop the washer, and stay off every drain, and they say it on the phone before leaving the shop. Next is the cleanout, and then the check most candidates skip: whether the blockage sits on the homeowner's lateral or in the municipal main. If the street side is backed up it is the city's line and the city's cost, and a plumber who makes that call at 9 p.m. instead of billing four hours has earned you a customer for a decade. Then containment, then clearing the line. On the contamination half, listen for treating sewage as what it is, a biohazard rather than dirty water. Strong answers keep the children out of the affected area, use gloves and eye protection, and are clear that the cleanup after the line is open belongs to a remediation vendor with the right equipment rather than to a shop vac and a mop. They photograph everything before touching it, because the homeowner has an insurance claim and that claim is easier with pictures. Be cautious with anyone who opens by pulling carpet, anyone who never checks the city side, and anyone who describes wading into sewage in street clothes. The gas half has one correct shape and you should score it pass or fail. Get everyone out, do not touch light switches, appliances, or a garage door opener, do not use a phone inside the building, call the gas utility and 911 from outside and well away, and shut off at the meter only if they are trained to and can reach it safely. A candidate who describes hunting the leak with soap solution inside an occupied house at night has told you something training will not fix quickly. Then ask the boring version of the same question: how far do they live from your service area, and what are they driving. After-hours coverage fails on drive time far more often than on willingness.

This work means crawlspaces, attics in summer, lifting water heaters with help, torch work, and sometimes a trench, all of which you would do with or without a reasonable accommodation. Tell me how you handle a trench deeper than five feet, what you do before digging near or cutting into a line you cannot identify, and what PPE you actually use. What hand tools do you own, do you have a truck, and do you hold a valid license with a record clean enough to be insured on a company vehicle?

What this assesses: Four filters in one question, and the safety half is the one that puts somebody in the hospital when you skip it. On trenching, the right answer is not that they are careful. It is a protective system, meaning a shield box, shoring, or a properly cut slope, at five feet and deeper under OSHA rules, a competent person on site with the authority to order people out, spoil kept back from the edge, and a way out close to wherever they are working. Be cautious with any version of "we jump in and jump out, it is only a few minutes," which is exactly how people die in trenches, and be cautious with a candidate who has never heard the phrase competent person. On unknown lines, strong answers call 811 before any dig with no exceptions and no judgment calls, and treat a pipe they cannot identify as live and possibly gas until proven otherwise. On confined spaces, listen for awareness that a sewer, a vault, or a deep pit can hold hydrogen sulfide and displace oxygen, and that the answer there is a permit and a meter rather than a held breath. On torch work, listen for clearing and shielding combustibles and a fire watch afterward, because those fires start after the truck pulls away. PPE should sound like a default rather than an occasion: eye protection every time something gets cut, gloves for drain work, hearing protection on a jetter or a saw. On tools, the trade norm is that the plumber owns hand tools and the company supplies the machines, the camera, the locator, and the jetter, so a candidate who expects you to supply their wrenches has not held this job, and one who claims to own a camera and a jetter is worth a follow-up about what they were running and for whom. Ask the physical and environmental part exactly as written, as demands of the job with the accommodation language, and stay out of health history entirely. On driving, ask about insurability rather than history in the abstract, because your carrier decides this one for you.

What is your on-call and overtime availability, including nights, weekends, and holidays, and what rotation could you actually work? What rate or pay structure are you looking for, do you have a drug screen or background check concern we should know about, and how soon could you start?

What this assesses: On-call is where plumbing hires quit, so surface the real rotation now instead of after the offer. Put the actual schedule in the posting and in this question, one week in four or every third weekend, and let candidates opt out while it is still free. Strong answers name a rotation they can work, accept that emergencies arrive at bad hours, and are specific about the constraints they do have, which is more useful to you than enthusiasm. Be cautious with a blanket "whatever you need," which collapses the first Saturday night a main backs up, and with hesitation on a routine drug screen most service companies require. Take the pay answer seriously and ask about structure rather than only the number. Many service shops pay a base plus a percentage of the ticket, and a plumber coming off straight hourly hears that as a pay cut even when it is not, while a plumber coming off commission hears a flat hourly the same way. If you are changing someone's comp model, explain it in the screen and not on the offer call. A licensed journeyman with a clean record and a backflow certification knows what the market pays and will leave over two dollars an hour, so a candidate who names a number above your band has done you a favor. On start date, a working plumber who offers to start tomorrow is either between jobs for a reason worth asking about, or is about to leave you the same way. Then score every candidate against the same [interview scorecard](/glossary/interview-scorecard) rather than reading answers one at a time, keep it a [structured interview](/glossary/structured-interview) so a commercial plumber and a residential service tech land on the same rubric, and run it as [asynchronous screening](/glossary/asynchronous-screening), because the plumber you want is in a crawlspace at two in the afternoon and is not taking your call. In this trade, [candidate drop-off](/glossary/candidate-drop-off) is the competitor you are actually losing to, and the shop that answers first usually wins.