Plumbing, Draining and Gasfitting Fundamentals
What the exam expects
Candidates must show command of the water supply, sanitary drainage and gasfitting systems covered by the NSW regulatory framework, including AS/NZS 3500 series, the Plumbing Code of Australia and the Gas Supply Act and Gas Supply (Safety and Network Management) Regulation. Know the terminology cold: fixture units, fixture discharge rates, graded drains, invert levels, water seals, venting, backflow prevention, and the difference between a boundary trap and an inspection opening.
Concepts to master
Understand hydraulic design: fixture unit loading, drain sizing, grades (typically 1:60 for DN65 and smaller, 1:100 for DN100 and larger in sanitary drainage), and why self-cleansing velocity matters. Understand venting: why every trap needs protection, the difference between individual, common and relief vents, and where an air admittance valve is permitted. For water supply, know pressure and flow requirements, backflow prevention device selection by hazard rating, and tempering valves for sanitary fixtures. For gasfitting, know gas types and their properties, pipe sizing methods, pressure test durations and acceptance criteria, flue clearances, and ventilation requirements for appliances.
Traps the exam sets
Questions love the near-miss: a grade that is too flat, a vent shared where it should not be, a pressure test held for the wrong duration, a regulator fitted on the wrong side of the meter, or a backflow device chosen for the wrong hazard level. Watch for wording about "minimum" versus "recommended" and about who may certify work. Another common trap is confusing nominal pipe size with internal bore.
Worked example
A rule of thumb for drainage grade: rise equals length divided by the grade denominator. A 12 m drain at 1:60 needs 12 ÷ 60 = 0.20 m, so the invert drops 200 mm over that run. Always check the downstream invert against the boundary trap and connection point before setting the upstream level.