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How to smoke test drains and sewers?

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smoke testing sewers

Smoke testing drains and sewers for leaks

smoke test sign Smoke testing in drains and sewers is a similar process to smoke testing in chimneys. However, instead of using the natural upward draw of a chimney to fill the enclosed space with smoke, a blower or fan is used to circulate the smoke down into the particular section of sewer so that observations can be made and information gathered about any leaks or defects there may be.
open sewer, manhole cover, smoke test

Step 1 – Open manholes

Open the manholes at either end of the section of sewer you want to test.

smoke testing sewers, block with sandbags, blower

Step 2 – Block lines

Use sandbags or covers to block the lines of the sewer that you are not testing.

smoke blower, fan, smoke test fan, manhole

Step 3 – Position smoke blower

Place the smoke blower over the open manhole and start it blowing down into the sewer line.

smoke filled sewer, smoke test

Step 4 – Light smoke pellets

Light your smoke pellets and place them on a grate beneath or in a holder on top of the blower. The blower will create a difference in pressure, forcing the smoke down into the sewer.

Smoke test, sewers, smoke plume

Step 5 – Search for plumes

The area around the section of sewer being tested should now be searched for smoke plumes.

broken pipe smoke test, smoke testing sewer

Step 6 – Mark plumes for fixing

Smoke plumes coming from properly fitted plumbing vents or around the rim of the manhole are normal and should be ignored.

However, smoke plumes coming from anywhere else are not normal and are probably a sign of a cracked pipe, an illegal connection or other defect and should be marked and fixed as soon as possible.

smoke leaking into house If smoke is found entering a house, then that residence either has defected plumbing or dry traps in the sinks.
smoke test, smoke entering house through dry traps

What is a “dry trap”?

In the U-bend of sink piping there is a small trap of water that stops potentially harmful sewer gases from entering your house. If a sink is not regularly used then it is possible for this water trap to dry up, leaving it open to odours and gases.

Cracked pipe smoke test smoke plume

Step 7 – Repeat smoke test

Once all defects have been located and fixed, repeat the smoke test until no defects remain.

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