Plumbing Systems and Installation
Core concepts
A plumbing system has two halves that must be designed together: the supply side (service pipe, meter, distribution mains, fixture branches, valves) and the drainage side (fixture drains, branches, soil and waste stacks, vent stacks, building drain, building sewer). Candidates should know the function of the main shutoff, the water meter, the check valve, the pressure-reducing valve, the vacuum breaker, the trap primer, the cleanout, and the vent through roof. Understand the difference between a soil stack (carries sewage) and a waste stack (carries other discharge), and why every fixture needs a trap with a liquid seal.
Traps in questions
Watch for questions that confuse the building drain with the building sewer: the drain is inside the building up to the foundation wall, the sewer is outside. Another common trap is the vent's purpose - venting protects trap seals from siphonage and allows smooth flow, it does not drain water. Also expect items on grade and fall, fixture unit loading, and the rule that no vent may terminate closer than the code-specified distance to a window or air intake.
Worked example
A rule of thumb for horizontal drainage pipe: slope at 1/4 inch per foot for pipe 3 inches and smaller (about 2 percent), and 1/8 inch per foot for 4-inch and larger pipe. For a 20-foot run of 2-inch pipe, fall = 20 × 1/4 = 5 inches. Check that the invert at the far end still connects above the main drain invert before you commit the layout.