Hollow and complex shapes such as toilets and washbasins cannot be pressed. They are cast: a liquid clay slip is poured into a porous mould, the mould draws water out of the slip, and a solid wall builds up against it.
Traditional moulds are plaster and rely on capillary suction. Pressure casting uses porous resin moulds and applied pressure, which shortens the cycle from hours to minutes and lets a mould be reused many more times.