In 2017, we published results from an experiment on a full-scale two-storey wastewater plumbing test-rig in which we used a model organism (Pseudomonas putida) to represent pathogens flushed into the system.4 Viable organisms were shown to be transmitted between rooms on different floors of a building, carried within the system airflow. Droplet fallout resulted in contamination of surfaces within the system and rooms. We also suggested causes of the wastewater plumbing system defects and presented a basic qualitative risk assessment for disease spread in buildings. One important factor identified was the interconnectedness of all parts of the building by the wastewater plumbing system and, therefore, the potential for contaminated air to travel throughout the building unhindered. We also identified the short-duration burst of contaminated air from the wastewater plumbing system that caused the cross-contamination.5