~10 years ago, a section of wooden gas main was found during an excavation in the warehouse district of Minneapolis. It was saved and now serves as a teaching aid. Of course it had been unused for ~60 years, but the pipe itself dated back to the 1870's. Way back from the wet-gas days.
Which ironically leads to the origin of another term: drip leg.
Conveyance of what we now call natural gas in the old days needed a bit of upkeep. Since a majority of the original gas mains were wood, water vapor was added to the gas to help keep the wood moist and swelled up to prevent leakage. (A sidebar to this for anyone in the Mpls area, this is why MinneGasCo/Relaint's pumping station is right off the river, east of 35W in Burnsville) The byproduct of this was the need to remove condensed water prior to using the gas at an appliance. Hence the drip leg was born.
Nowadays it may be called a dirt leg or sediment trap. It is still required prior to all controls/fixtures up here in the north, at vertical-to-horizontal changes in direction and when gas enters from an unconditioned space to a conditioned space.
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