Plumbing Systems: Planning, Installation, Testing and Servicing
The Red Seal Plumber exam treats planning, installation, testing and servicing as one integrated domain. Questions move from drawing and code interpretation through rough-in, final connection, pressure testing and repair decisions. Expect DWV and water-distribution sizing, venting, support, clearances, test pressures and service diagnostics.
Plan from code and drawings
- Verify scope against approved drawings, specifications and the local plumbing code; confirm permits and inspection stages before work begins.
- Establish fixture units, trap sizes, developed length, static pressure, water-heater location, backflow/backwater protection, and conflicts with structural, electrical and HVAC work.
- Size drainage by fixture units and allowable slope; size vents by fixture-unit load and developed vent length; size water pipe by fixture units, equivalent length and pressure loss.
- Set rough-in elevations for fixtures, floor drains, cleanouts, sleeves, hangers and firestopping, and confirm access is maintained.
Install to grade and support
- Horizontal drainage: 2% (1:50) for 3 in and smaller, 1% (1:100) for 4 in and larger. Keep trap arms and vents within code distance; provide cleanouts at stack bases and direction changes.
- Support pipe at code spacing, isolate dissimilar metals, allow for thermal expansion, and install shutoffs, arrestors and freeze protection.
Test, commission and service
- DWV: hydrostatic test to the code-required head, or an approved air test where permitted. Water distribution: hydrostatic test at 100 psi or 1.5 times working pressure, whichever is greater, for the required duration.
- Use a calibrated gauge, isolate the test section, inspect every joint, record results, then retest after repairs. Service work requires diagnosis, isolation, drain-down, approved materials, purging and potable-line disinfection where required.
Worked example
A 4 in PVC drainage run is 28 m long at minimum grade. Fall = 28 × 1/100 = 0.28 m. If the upstream invert is 102.450 m, the downstream invert is 102.450 − 0.280 = 102.170 m. Using 1/4 in/ft would overstate the fall and set the downstream invert too low.
Traps that cost marks
- Applying 1/4 in/ft to 4 in and larger pipe instead of 1%.
- Sizing water pipe from fixture count alone, ignoring developed length and pressure loss.
- Forgetting venting, trap-arm distance or cleanout access.
- Testing with an uncalibrated gauge or without isolating the section.
- Failing to retest after repair or to account for thermal expansion.