Many of the important aspects of maintaining a system’s integrity by preventing sewer gases from entering living spaces, the water trap seal and system venting, had already been introduced and much work on improving the system’s response to the inevitable pressure fluctuations encountered in a fluid transport system were well under way.

This paper explores the work of early innovators in the field and tracks developments through the 20th Century to the present day and considers how this early work has often been sidelined in favour of less scientific design techniques in codes and standards. It is hoped that this paper will highlight the early work of those attempting to create a safe, hygienic environment for people, for the first time. This work should be remembered in a favorable light, not least because of their commitment in the face of opposition, but because their observations were based on the sound engineering and scientific methods often absent from deliberations in the industry today.

Introduction
Building drainage system research and modelling is often concerned with physical phenomena on a minute scale. This author’s paper contribution to the CIBW62 symposium in Taiwan in 2006 considered the risk of trap seal depletion due to solids falling down a vertical stack, with the duration of the resulting air pressure transient measured in milliseconds. With the introduction of modern technologies such as the positive air pressure attenuator comes a need to measure performance over a very short timescale, again measured in milliseconds. In stark contrast to the flows found in public sewer networks, most flow scenarios in building drainage systems can be simulated in numerical models using total simulation times of less than one minute. Scale is an important issue in engineering science and building drainage systems are no exception. Shorter time scales and larger physical variables (such as pressure, velocity) are inevitable the closer to the point of system entry one looks.

The modelling of a building drainage system operation focuses mainly on the derivation of boundary equations for inclusion in numerical models, a process which forces the researcher to determine the relationships involved forensically and, in many cases, in an isolated manner. The combination of small time scales and the need for accurate system boundary information encourages researchers to look at a system on a ‘micro’ level.

This paper takes a step back from this approach and considers some of the ‘macro’ implications of building drainage system design, but from a historical perspective. It is hoped that this approach will highlight that some of the important issues facing the drainage research team today, have faced researchers since the birth of modern sanitary engineering, arguably considered to be in the 19th Century. The myths alluded to in the title of this paper are in effect the superstitions and mis-information which have dogged this area of engineering, much more than any other. The ‘legends’ refer to seminal work by early investigators, often forgotten, but which have proved their worth in modern times.

It should be noted that the issue of sanitation provision follows particular cultural and geographical standpoints, and while every effort has been made to make this paper as general as possible, it is inevitably written from a European/American/Western perspective. This is in part due to the influence that modern gravity fed drainage systems have had on world sanitation, but also in part due to the background of the author.