Just a head’s up and sharing only because I’ve been jumped on by folks smarter than me.
Review codes, definitions, etc. of: drip legs, dirt legs, sediment traps.
They are often used/interchanged all over the place and different parts of the country have their own familiarity.
Drip legs - Typically used when dealing with ‘wet’ gas and in code books they are used at/near/before the gas meter to a property.
Dirt legs - Used at appliance cutoff valve in front of manifold of same. More often a regional/local term.
Sediment trap - The actual correct term for the device (also known as a Dirt Leg) installed before the manifold at an appliance.
Like JP noted I review for manufacturer’s requirements. IRC has required them for years and years and years … in the D/FW market the local AHJs seldom enforce installation of same, yet they don’t ‘exclude’ them on their municipal documents.
IRC requires them at: Furnaces and Water Heaters.
Sediment Traps - From IRC:
IRC - International Residential Code: G2419.4 (408.4) Sediment trap. Where a sediment trap is not incorporated as part of the gas utilization equipment, a sediment trap shall be installed downstream of the equipment shutoff valve as close to the inlet of the equipment as practical. The sediment trap shall be either a tee fitting with a capped nipple in the bottom opening of the run of the tee or other device approved as an effective sediment trap. Illuminating appliances, ranges, clothes dryers and outdoor grills need not be so equipped.
Drip Legs - From IRC:
G2419.2 (408.2) Drips. Where wet gas exists, a drip shall be provided at any point in the line of pipe where condensate could collect. A drip shall also be provided at the outlet of the meter and shall be installed so as to constitute a trap wherein an accumulation of condensate will shut off the flow of gas before the condensate will run back into the meter.
Drips, often referred to as “drip legs,” are distinct from sediment traps. Modern gas supplies and distribution systems are typically dry; thus, drips would be required only when recommended by the gas supplier.
G2419.3 (408.3) Location of drips. Drips shall be provided with ready access to permit cleaning or emptying. A drip shall not be located where the condensate is subject to freezing.
A drip is not the same as a sediment trap; they are required for different reasons (see Section G2419.4).
What also makes my being “so picky” frustrating is that many manufacturers also label some of their drawings of the trap being installed adjacent to the water heater/furnace, etc… and they then ‘mis-label’ it as a “drip leg”.
Sometimes you just can’t win … and in the overall scheme of things it is a very small item. Not something to fall on a sword over.
Likely more than anyone wants to know. 
And then there are the rules that govern CA. I can’t even begin to address those details.
Cheers,
Nolan Kienitz