The drainage systems in many existing buildings were not designed properly, and as a result they have problems with breached trap seals.

A recent example is the iconic Taipei 101 building in the Xinyi District of Taipei. This 101-storey building experienced positive transient pressures from floors 6 to 12. Evidence could be seen of bubbling and self-siphonage of toilets at those floors. Local intervention was required, and the problem was solved using the P.A.P.A. (Positive Air Pressure Attenuator) system of active ventilation.

However, many existing buildings face similar issues that have not been resolved.

Doing nothing is not an option, as a badly-designed drainage system can cause discomfort for inhabitants through bubbling noises and bad smells. The related health risks are more serious in nature, and require immediate investigation and the application of troubleshooting solutions.