Final answer:
To prevent health and environmental hazards, abandoned building sewers should be plugged or capped, a practice that stems from the engineering advancements during the Great Stink in London, leading to the creation of modern sewer systems such as the one designed by Joseph Bazalgette.
Step-by-step explanation:
Every abandoned building sewer should indeed be plugged or capped to prevent the entry of dangerous gases into buildings, avoid contamination of soil and groundwater, and to prevent it from becoming a breeding ground for pests. This practice was not always standard, as historical events like the Great Stink of London in 1858 showed the importance of a well-designed sewer system.
The London sewer system was a necessary response to the increasing urban population and industrial activities. Before its construction, waste often ended up in the River Thames, creating a public health hazard. The new system designed by Bazalgette carried sewage downstream and was so robust that parts of it are still in use today. Cities around the world followed suit, building elaborate drainage systems to manage their waste.