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Siphonic flush


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(Picture: Hugh Sainsbury/Crossness Engines Trust)


Superficially, the Closet of the Century resembles an older wash-down closet. However, rather than simply being flushed away by the force of the flush, water and waste from the pan was sucked away to the sewers by siphonic action. The result was a quieter, more effective flush and, usually a larger volume of water in the pan, drowning solid waste and masking smells.

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(Picture: Patent, courtesy of British Library)


The diagram from Jennings’ patent application of 1894 shows in simple form how the siphonic action that flushed away water and waste was created. The closet has two water-traps – one right below the bowl, and another lower trap connected by a long vertical pipe. When the flush reached the pan, the water level tipped over the weir (n) into the vertical pipe, creating a siphon effect that sucked away the contents of the pan. The dual trap ensured that the water seal was never broken, so smells couldn’t emerge into the room through the pan.


Siphonic-action closets were developed in the US from the mid-19th century. John Gray patented a siphonic closet in 1855, and another was patented by John Randall Mann in 1870. But the concept burst onto the British market in 1894, when three manufacturers launched models with different mechanisms.


Jennings’ dual-trap siphonic toilet was effective, but expensive and complicated to install; its pipework was also best enclosed within woodwork, rather than standing alone. Twyford’s single-trap stand-alone Twycliffe (shown below) featured two auxiliary inlets that injected jets of water into the base of the pan and directly into the trap to start the siphonic action; this was simpler to install than Jennings’ model, but the inlets were prone to blockage. In the same year, Shanks patented the Barrhead single-trap closet, which directed a jet of water into the trap.

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(Picture: Clive Hurst/Licenced under CC BY-NC 2.0)


The siphonic system was doubtless effective and, because the flush didn’t rely on a volume of water cascading down with force, it enabled operation with low-level close-couple cisterns rather than ones attached to walls at a high level. Siphonic toilets remain popular in the US. However, these early models were more expensive, complicated and liable to clogging than simple wash-down closets, which became widespread in homes across Britain over the following decades.

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