Installing a vanity unit couples three independent subsystems: structural fixing of a floor-bearing carcass that is levelled and merely restrained laterally to the wall, a pressurised supply branch terminating in isolating service valves and flexible tails to the tap, and a gravity waste branch in which a water-sealed trap and a continuously falling pipe run carry discharge to the soil stack. The governing principles are that pressurised jointing (compression olives, push-fit seals with inserts for plastic tube, braided-hose rubber washers) seals by controlled compression and must be isolated and drained before it is opened, whereas waste jointing seals only against atmospheric-pressure flow and depends on gradient rather than tightness, with the trap's water seal providing the barrier against drain gases. The topic belongs to domestic sanitary plumbing and bathroom fit-out within building services, and it illustrates the discipline's general sequencing rule — rough-in the concealed services before final fixing, because access is progressively lost.
Installing a vanity unit couples three independent subsystems: structural fixing of a floor-bearing carcass that is levelled and merely restrained laterally to the wall, a pressurised supply branch t…