|Description:||This historic 1941 diagram, which had been digitally enhanced and colorized, illustrated a method of altering tank-type flush toilets, in order to prevent "back-siphoning". Back-siphoning is the sudden loss of pressure within a plumbing system that could allow dirty water to be sucked into the supply pipes, which would contaminate the water system's clean water supply. Such a phenomenon could involve just the plumbing in a single house, if it was on its own well, or it could occur inside a municipal water system.|
The purpose of these images and the accompanying training was focused on protecting water supplies from bacterial contamination due to incorrect disposal of waste, such as sewage, in order to prevent water-borne diseases. The descriptive information accompanying this drawing referred to a governmental publication, which contained instructions describing how to correctly place and build such a device. The specific citation was, “Minnesota Department of Health, Division of Sanitation, Manual of Water Supply Sanitation, 1938, Section 8, p. 14”.