Eva Crossan, of Stirling, asks :-

How do poos and wees get flushed down the toilet?

Brian Turner, a wastewater engineer with the Dunedin City Council, responds.

How to effectively handle sewage has been a problem for thousands of years. Early Victorian cities were warrens of filth. Toilets were no more than holes or cess-pits in the ground close to housing and often shared by whole streets. In heavy rain these cess-pits overflowed into the street. Factories would also just throw rubbish and waste into the streets until they ran as a liquid stream of slime. In many parts of the world these conditions still prevail.

By the early 19th century people began to realise that there was a link between human waste, disease and drinking water, particularly so for the disease called cholera. By the 1850s various flush toilets and water closet systems, coupled with sewerage piping systems and early wastewater treatment plant, were seen as an answer to remove human waste away from houses. However few water closet systems worked properly.

Some of the earliest designs date back to the 16th century and even King Minos at Knossos in Crete, some 4,000 years ago, had a latrine with a reservoir of water to flush away the royal waste. However it was not until the late 1870s that an efficient and workable toilet waste flush system was developed.

Thomas Crapper, a London based Sanitary Engineer, was the first to perfect a float, metal arm and a siphonic action to empty the water reservoir and thus flush the toilet. This system Thomas Crapper perfected is still virtually the same as we use today - you can see how the float and siphonic system works by taking the lid off the cistern.

What is for us a device that we almost take for granted helps to flush away the `poos and wees'and transport our waste to the wastewater treatment plant where it can be safely treated before final disposal.

There is only a very small amount of solids and `poos and wees' in the sewerage drainage system compared to the water and so the human waste is safely taken away from houses in sewerage pipes. These flow to their lowest point, where it is pumped to the wastewater treatment plant.