Before testing, pipework will be inspected for any obvious leaks and breakages. This will likely be done with the help of CCTV drain surveying. If obvious damage is found, this will need to be fixed prior to any air tests.
If no obvious breakages are found, a section of the pipe will be closed off and isolated. This is typically a section between two maintenance holes for easier access. The pipe will be fully drained prior to the test, and all spigots and drains will be closed off, so no external sources are able to interrupt the test. Drainage usually occurs two days before testing.
Air is then pumped into the drainage system, and the pressure is monitored using two pressure gauges. Changes in pressure are recorded and used to identify potential issues and leaks within the drain.
If more clarification is needed, a water test will be used to verify these results. When the damage is located, the correct maintenance work will be attempted, and the pipe will then be tested again to ensure the repairs have completely fixed the issue.