Sounds like the gas trap test. This is copied from the 2000 international
P2503.5.2 Finished plumbing. After the plumbing fixtures
have been set and their traps filled with water, their connections
shall be tested and proved gas tight and/or water tight
1. Water tightness. Each fixture shall be filled and then
drained. Traps and fixture connections shall be
proven water tight by visual inspection.
2. Gas tightness. When required by the local administrative
authority, a final test for gas tightness of the DWV
system shall be made by the smoke or peppermint test
2.1. Smoke test. Introduce a pungent, thick smoke
into the system. When the smoke appears at
vent terminals, such terminals shall be sealed
and a pressure equivalent to a 1-inch water
column (249 Pa) shall be applied and maintained
for the period of inspection.
2.2. Peppermint test. Introduce 2 ounces (59 mL)
of oil of peppermint into the system. Add 10
quarts (9464 mL) of hotwater and seal all vent
terminals. The odor of peppermint shall not be
detected at any trap or other point in the system.
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