Ten 306A Plumber questions in the format of the Red Seal exam: four options, one correct answer, no trick questions. They are free to use, print and share. There is nothing to sign up for on this page.
01How to use these
The questions come from the TicketPrep 306A bank and are spread across the exam's work activities in the order and roughly the proportion the Red Seal Program publishes for this trade: A (performs common occupational skills), B (prepares and assembles tube, tubing and pipe), C (installs, tests and services sewers, sewage treatment systems and drainage, waste and vent (dwv) systems), D (installs, tests and services water service and distribution), E (installs, tests and services fixtures, appliances and water treatment systems), F (installs, tests and services low-pressure steam and hydronic systems), G (installs, tests and services specialized systems). Answer each one before opening the explanation. Every explanation covers all four options, because on the real exam the wrong options are written to be plausible, and knowing why they are wrong is most of the skill.
- Pace. The exam allows four hours for 125 questions, so about 1 min 55 s per question. Try these at that pace.
- Print. The printed version shows the questions and the answer key without the explanations, so it works as a handout. Download PDF
- Mark. The pass mark is 70 percent on every Red Seal trade; seven of ten here is the same bar.
02The questions
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On a strip-mall tenant fit-out, the current mechanical drawing shows a floor drain where the current structural drawing shows a concrete grade beam. Both sheets are the latest revision. What do you do?
- Leave the drain out and let the inspector decide at final
- Submit an RFI to the designer and wait for direction
- Move the drain to where it fits and note it on the as-builts
- Install it as the mechanical drawing shows; it is your trade's sheet
Show the answer
B. Correct. When current contract documents conflict, a request for information (RFI) goes through the proper channel to the designer, and the drain is installed once the answer is issued. It protects the structure and leaves the decision with the people responsible for the design.
Why not the others
A. Leaving out a drawn drain pushes a design question to the end of the job, after the slab is poured. The inspector enforces the code but does not resolve drawing conflicts; raise an RFI now.
C. Moving a floor drain changes the area it serves, the floor slope to it and possibly the trap and vent layout. That is a design decision made through an RFI, not a field choice.
D. The mechanical sheet does not override the structural one, and a grade beam is not cut to suit a drain. A conflict between current sheets is resolved through an RFI.
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A new 4-inch (100 mm) PVC building sewer must connect to an existing vitrified clay tile sewer that has a different outside diameter. How is the connection made?
- A standard no-hub coupling sized for the PVC
- Mortar the PVC spigot into the clay bell
- Solvent-cement the PVC spigot into the clay bell
- A listed transition coupling sized for each pipe's OD
Show the answer
D. Correct. A transition coupling has a rubber sleeve moulded to fit a different OD at each end, with stainless clamps (and a shield or shear band where required) to hold alignment. It is listed for joining the two materials. Bed both pipes firmly so the joint does not shear.
Why not the others
A. A standard coupling is sized for one OD; on a larger clay OD it will not fit, and on a smaller one it cannot clamp tight enough to seal. A transition coupling has a sleeve made for each pipe's OD.
B. Mortar joints were used on old clay tile, but mortar does not bond to PVC and cracks with any movement, letting in roots and water. Use a listed transition coupling sized for each OD.
C. Solvent cement only fuses compatible plastics; it will not bond to clay. Joining different materials takes a listed transition coupling sized for each OD.
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On the annual service of a normally open backwater valve in a seniors' residence basement, you remove the access cover. What does the service include?
- Coat the flap and seat with petroleum grease so debris cannot stick
- Replace the valve body every year, since its parts cannot be serviced
- Wire the flap open so it cannot stick shut and block the drain
- Clean the flap and seat, check it swings and seats, renew the seal
Show the answer
D. Correct. Clear debris from the flap and seat, confirm the flap moves freely and closes fully, check the cover gasket or compression seal and replace it if worn, then refit the cover and run water to confirm flow. Wear gloves and eye protection for the biohazard, and record it in the service report.
Why not the others
A. Petroleum grease can swell or degrade the rubber flap and seal, and it holds grit rather than shedding it. The flap and seat are cleaned, checked and, if needed, fitted with the maker's parts.
B. Backwater valves are built to be serviced through the access cover: flap, seat, gaskets and cover seals are replaceable parts. The body is replaced only when it is damaged.
C. A flap wired open cannot close when the sewer backs up, which defeats the valve's only purpose. A normally open valve is already open for flow; the service makes sure it can still close.
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A distribution box feeds four equal leaching trenches on an acreage. How do you confirm it is set correctly before backfilling?
- Check that it slopes 1 in 50 toward the farthest trench
- Check that the inlet is lower than the outlets
- Check that the lid is watertight; the outlets even out in use
- Run water in and check it leaves all four outlets equally
Show the answer
D. Correct. With the box on a firm, compacted base, run water in and watch that it reaches and leaves all four outlets at the same level; adjust with the outlet levellers or reset the box until it does. An uneven box overloads one trench.
Why not the others
A. Any slope in the box sends more effluent to the low outlets, overloading those trenches while others stay dry. The box must be level so every outlet sits at the same height.
B. An inlet below the outlets would hold effluent back in the line from the tank. The inlet enters above the outlets, and the outlets are set level with one another.
C. A tight lid keeps surface water out, but outlet levels do not correct themselves; an uneven box keeps favouring its low outlet. Test with water before backfilling.
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In a house in a northern community, the bathroom lavatory gurgles and loses part of its trap seal whenever the WC flushes, but only during the coldest weeks of winter. The lavatory's vent joins a 1½-inch (38 mm) vent that passes through the roof unenlarged. What is the most likely cause?
- Evaporation of the lavatory's trap in dry winter air
- A leaking WC flapper refilling the bowl
- Frost closing the small vent terminal, cutting off air
- A partial blockage in the lavatory's trap arm
Show the answer
C. Correct. Warm, moist vent air freezes on the inside of a small terminal in extreme cold until it closes. With no air from the vent, the WC's discharge pulls the lavatory's seal (induced siphonage). The cure is the code's frost-closure protection: enlarge the vent at least one size, to not less than 3 in, just before it penetrates the roof.
Why not the others
A. Evaporation is slow and has nothing to do with the WC flushing. A seal lost at the moment of a flush is siphonage, caused here by the frozen vent.
B. A leaking flapper wastes water and makes the tank refill, but it does not pull a nearby trap's seal, and it has nothing to do with the weather.
D. A blocked trap arm makes the lavatory drain slowly all year and does not depend on the WC flushing or the weather. The link to extreme cold points at the vent terminal.
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A strip-mall tenant's PRV is set to 345 kPa (50 psi). With no water in use overnight, the downstream gauge climbs to 621 kPa (90 psi), the same as the street pressure, and stops there. There is no water heater or other heat source on this line. What is the most likely cause?
- Water hammer from quick-closing valves in the tenant space
- A worn or fouled PRV seat letting street pressure creep through
- A clogged strainer ahead of the PRV
- Thermal expansion in a closed system
Show the answer
B. Correct. With no flow, a healthy PRV closes tight at its set pressure. A seat that is worn, scored or holding debris lets water creep through until the downstream side equals the street pressure, which is exactly where the gauge stopped. Clean the strainer and rebuild or replace the PRV.
Why not the others
A. Hammer produces brief spikes when valves close during use. A slow, steady rise overnight with no use, levelling off at street pressure, is PRV creep.
C. A clogged strainer starves the PRV and lowers downstream pressure during flow. It cannot raise the static pressure to street level.
D. Thermal expansion needs heated water, and this line has no heater; it would also push pressure above street pressure, not stop at it.
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You are connecting the water line from a drilled well to a house. The frost depth is 1.8 m (6 ft), and the provincial well regulation requires the casing to extend at least 40 cm (16 in) above finished grade with a sanitary cap. How is the water line brought out of the casing?
- Into a buried well pit built around the casing below frost
- Through a hole cut just below grade, sealed with caulking
- Through a pitless adapter in the casing below frost depth
- Out over the top of the casing, then down into the trench
Show the answer
C. Correct. A pitless adapter (or pitless unit) seals through the casing wall below the frost depth, so the line leaves the well where it cannot freeze while the casing stays sealed and above grade. The drop pipe hangs from the adapter's removable half, so the pump can be pulled from the top.
Why not the others
A. Well pits flood and let surface water reach the casing top, so provincial well regulations restrict them; the pitless adapter replaced them for new drilled wells.
B. Just below grade is inside the frost zone, and a caulked hole is not a sanitary, watertight seal against surface water. Use a pitless adapter below frost depth.
D. A line over the top runs through the frost zone and needs a hole in the cap, breaking the sanitary seal. The pitless adapter exists to exit below frost.
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A new residential dishwasher drains into the kitchen sink's disposer, and the AHJ accepts a high loop instead of an air gap. How is the drain hose run?
- Into the sink's vent pipe inside the wall cavity
- Up to the underside of the counter, then to the disposer inlet
- Into the trap arm on the sewer side of the trap weir
- Along the cabinet floor straight to the disposer inlet
Show the answer
B. Correct. The loop lifts the hose above the sink's flood level, so a blocked or backed-up sink cannot siphon or flow waste back into the dishwasher. Knock out the plug in the disposer's dishwasher inlet before connecting; where the AHJ requires an air gap, the hose goes to a deck-mounted air gap instead.
Why not the others
A. A vent is not a drain; discharging into it can flood or block the vent and cause trap siphonage. The dishwasher drains through the disposer or a tailpiece wye above the trap.
C. A connection on the sewer side of the trap bypasses the trap seal, letting sewer gas into the machine and the kitchen, and it gives no backflow protection. The discharge goes into the disposer or a tailpiece above the trap.
D. A hose lying low lets sink waste run back into the dishwasher when the sink is full or the drain is blocked. The loop (or an air gap) is what provides the protection.
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A new three-zone baseboard system in a seniors' residence is being purged through a purge station on the return. Which sequence clears the air most reliably?
- Open all three zones together so one flow sweeps them all
- Run the circulator and let the automatic vents do the work
- Close the purge-station valve, flush one zone at a time to a hose
- Close the fill valve and open the purge so pressure pushes air out
Show the answer
C. Correct. With the purge-station isolation valve closed, fill water must travel out through the one open zone and back to the purge valve, pushing air ahead of it to a drain until the stream runs solid; then close that zone and open the next. Afterwards the separator and vents clear the remaining microbubbles.
Why not the others
A. Water takes the easiest path: the shortest zone clears and the others stay air-bound. Purge one zone at a time so the full fill flow goes through each.
B. Automatic vents remove air that reaches them, but a zone full of air may not circulate at all. Forced-flow purging clears the loops first; vents finish the job.
D. With no make-up, opening the purge just drops the pressure and can draw air in at vents. The fill valve feeds while the purge valve discharges.
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A plumber is laying out a sloped compressed-air main around a farm equipment shop, with drops to hose reels on the building columns. How should each drop be taken off the main?
- Off the top in a swan-neck, with the outlet tee above a drain leg
- Off the bottom of the main, so the air flows straight down to the reel
- Off the side of the main at the pipe's centreline height
- Off the top, with the hose outlet at the very bottom of the drop
Show the answer
A. Correct. Taking air off the top of the main leaves condensate and scale running along the bottom to the drip legs. Each drop ends in a drain leg with a drain valve, and the hose outlet tees off above it, so water that reaches the drop collects below the outlet. A filter-regulator-lubricator at the tool finishes the job.
Why not the others
B. Condensate and pipe scale in the main flow along the bottom and would pour straight into the drop, the hose and the tools. Drops are taken off the top of the main.
C. A side takeoff still picks up water carried along the pipe wall and any that pools when the main is loaded. The rule is off the top, turned down in a swan-neck, with a drain leg at the bottom of the drop.
D. Taking off the top is right, but an outlet at the very bottom of the drop collects whatever water reaches the drop and sends it down the hose. Put the outlet tee above a drain leg with a drain valve.
03Answer key
| Question | Answer | Work activity |
|---|---|---|
| Q1 | B | Performs common occupational skills |
| Q2 | D | Prepares and assembles tube, tubing and pipe |
| Q3 | D | Installs, tests and services sewers, sewage treatment systems and drainage, waste and vent (DWV) systems |
| Q4 | D | Installs, tests and services sewers, sewage treatment systems and drainage, waste and vent (DWV) systems |
| Q5 | C | Installs, tests and services sewers, sewage treatment systems and drainage, waste and vent (DWV) systems |
| Q6 | B | Installs, tests and services water service and distribution |
| Q7 | C | Installs, tests and services water service and distribution |
| Q8 | B | Installs, tests and services fixtures, appliances and water treatment systems |
| Q9 | C | Installs, tests and services low-pressure steam and hydronic systems |
| Q10 | A | Installs, tests and services specialized systems |
04More free questions
For the 306A exam itself, the 306A exam guide covers the work activities, their weights and how the exam is scored, and the 306A Plumber practice exam page describes the full TicketPrep 306A question bank. The same free format is available for the other 11 trades, plus the free guides on the pass mark, question counts, exam day and how to study.
How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.