Plumbing overflow

An overflow device for use with a plumbing installation, a basin or a bath, the overflow device comprising:

• a body adapted to be positioned adjacent an exterior of the plumbing installation, the body comprising a first passage, a second passage, a third passage, and a cap covering an upper end of each passage, wherein the first and second passages are divided by a first passage member and wherein the first and second passages together with an interior volume of the cap form an inverted-U shaped siphon passage, wherein the first and second passages define an inlet and an outlet joined by the inverted-U shaped siphon passage;
• and
• the third passage together with a part of the cap forms an air valve, wherein an upper portion of the cap defines an entry port, the entry port being separated from an upper end of the first and second passages by an inverted weir, wherein the inverted weir extends downwardly from an upper end of the third passage such that its lowest point is below an upper end of a second passage member dividing the third passage from the first and second passages, and wherein the air valve is operable to communicate ambient air to a top of the inverted U-shaped siphon passage and wherein the air valve is arranged to close when water level in the plumbing installation increases to a predetermined overflow level thereby creating a siphon effect and wherein the air valve is arranged to open when the water level in the plumbing installation decreases from the predetermined overflow level thereby breaking the siphon effect.