A principal concern when designing a central vacuum system is avoiding situations likely to cause clogging of the tubing with debris such as toothpicks, hairpins, needles, or similar-shaped objects. The most important safeguard is at the vacuum inlets, which are intentionally designed with a tighter radius of curvature than any other bends in the system. This is done to ensure that if any vacuumed debris becomes stuck, it will jam right at the inlet, where it is easiest to discover and to remove. Well-designed central vacuum tubing rarely or never clogs unless severely abused (e.g. vacuuming wet plaster, wet flour, or other sticky substances).
The wall inlets are connected to the power unit by tubes that can be run inside walls, or through vertical pipe chases, closets, the attic, basement, or the cold air return ducts (if permitted by building code). In new construction, the vacuum tubing is usually installed during a "rough-in" phase once the building interior framing is complete, after other in-wall utilities (e.g. plumbing, HVAC, electrical, etc.), and just before drywall, paneling, or other surface finishes are installed. Strictly speaking, vacuum tubing should probably be installed before cabling, since routing of wiring is usually less constrained than tubing. In a similar manner to plumbing and electrical fixtures, the vacuum inlet fittings and final connections are installed in a finish phase, after the wall finishing is complete.