How does the home plumbing system work

Plumbing is one of those marvels of modern living: The more optimally it functions, the less we notice it.
But how does water rise to a home's upper floors to flow at the turn of tap?
In a word, pressure.
It's generated by exploiting Pascal's insight that water pressure increases with depth (not overall volume).
Water towers achieve these depth through elevation; often sited on hills or on the roofs of tall city buildings, a tank is raised many feet in the air.
The weight of the water column drives downward, pressing water through supply lines with enough force to lift it to upper floors.
That said, people on the ground floor usually get better water pressure than people on the higher floors.
Wastewater leaves the home via an entirely separate system that depends on gravity; all pipes are angled to let the water drain down.
Among common plumbing fixtures, the humble toilet is probably the most elaborate.
It flushes by a siphon effect.
Push the flush handle, and a chain lifts open a valve in the toilet tank, dumping water into the bowl.
The water enters quickly enough to flood the toilet's drainpipe, which curves up and then down as it leaves the bowl.
As in any siphon, the flow downward creates a low-pressure area at the top of the pipe's curve, which sucks the rest of the water from the bowl, emptying it into the waste stream.