Plumbing and Piping Systems
Foundations
Piping questions test the relationship between pipe types, routing preferences, and system classification. A pipe type bundles material, schedule/display, and fitting preferences for a given shape and size range. System classification (domestic hot water, domestic cold water, sanitary, vent, hydronic supply/return, fire protection) governs which pipes may connect and how systems appear in the System Browser.
Slopes, offsets, and verticality
Sloped piping is a frequent exam topic. Slope is set per pipe segment or via the Slope Editor; the slope value and the elevation interact, so changing slope on a run can move endpoints. Vertical pipes connect levels; horizontal offsets are set in section or via the properties palette. Know that a pipe's "Middle Elevation" versus "Start/End Offset" behave differently, and that justification (e.g., bottom of pipe) shifts the physical location relative to the centerline.
Plumbing specifics
Plumbing fixture families host connectors; a fixture must be connected to a pipe system for flow to aggregate. Sanitary and vent systems rely on correct classification, and gravity systems need slope. Pipe sizing uses fixtures or methods such as Hunter's curve in engineering practice - Revit itself sizes via the pipe sizing dialog and methods you configure, so know the tool rather than memorizing code tables.
Traps and rule of thumb
Traps include: assuming pipe insulation changes system classification (it does not), confusing pipe placeholder with real pipe (placeholders carry no flow geometry and must be converted), and expecting automatic slope to apply to fittings without proper routing preferences. Rule of thumb: if a system shows zero flow, check fixture connectors first, then classification, then slope.