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I understand how this will be perceived by some since I’m not a licensed plumber. However, I’m not going to pay a licensed plumber $2000 for installing gas pipe. (Yes, I did go through the effort of getting an on-site estimate from a licensed plumber.) It’s just not going to happen. (Yes, I understand the consequences.)

I need to install gas line (black steel pipe) in order to supply gas for a gas dryer. I’ve removed the drywall and see all the pipe in the wall that I will be working on. I’ll need to replace a few tees, replace some pipe, add some pipe, and so on. I’ll be using pipe dope (Rectorseal) for the fittings, drilling holes through the studs, and so on. I will also purchase a manometer and hook it up to perform a pressure test (not relying on liquid and bubbles).

I’m not going to do it until I'm confident that I'm doing it as safe as I personally can (personally, as in without paying a licensed professional).

My question is: when I shut off the valve at the gas meter, if I just open the gas line, there will still be gas in the lines that will escape. In order to perform this procedure most safely, what is the best way to evacuate gas from the gas lines prior to opening the gas lines? Should I just shut off the valve at the gas meter and then run the water heater until the pilot light goes out (observed by visual inspection)? (I don't have a gas range, so I can't run a stove and watch the burners.)

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  1. Do not use pipe dope. The secret to making gas tight fittings is to screw in each connection until only one or two threads are showing. Yellow Teflon tape makes this easier, but it is not a requirement. It can take up to 24 hours for the steel pipe to seal up, so do not expect it to immediately be gas tight. A 16 inch (or longer) pipe wrench also makes this easy, but it is still quite a workout.

  2. Yes, there will be natural gas in the line. It should be at a pressure of about seven inches of water column (equivalent to 1/50 atmosphere, 0.02 bar, and 0.25 psi). If there is a really long and fat pressurized pipe (50+ feet of 3/4 inch) in the system, opening could release a few cubic inches of gas. But it is going to rapidly dissipate and float away. Natural gas is buoyant; propane sinks and accumulates in low places. Personally, I wouldn't worry about gas in the line. Just opening a nearby window is more than enough. (Of course, I don't smoke either.)

There is no reason for a plumber to lay pipe. This is something anyone can do. Homeowners are, in my experience, more likely to do a better job because the professionals don't have to live with the installation.

As long as you do a good pressure test, you can assure yourself and your loved ones that it was done well.

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    Pipe dope acts as a lubricant, which allows you to tighten the joint adequately. Without it, you're not likely to get the fittings tight enough. Tape dope should work just as well as paste dope, as long as the tape is designed for gas fittings. You'll want to be cautious of cheapo fittings, as they may be manufactured poorly and could crack during tightening.
    – Tester101
    Commented Aug 21, 2016 at 15:24
  • So I assume 1) once you close the shut-off valve at the meter 2) pilot lights will remain ON until all gas in the line is combusted 3) opening up a line at an appliance will release any further residual gas in the lines?
    – farinspace
    Commented Oct 17, 2023 at 21:35
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Only use dope and plenty of it. I’ve seen Teflon fail, and I always see leaks when Teflon and dope are used on any ng or propane line. Its a fact. I use dope only on gas lines, and tape and dope on brass or galvanized WATER lines. I’ve been told also by plumbers with way more experience than myself to never use Teflon on gas lines for this reason. Please be safe and bubble test the bell out of every fitting.

PS: pro flex is very easy to use if prepared correctly

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    This doesn't address the question, which is how to flush the pipes before working on them.
    – Chenmunka
    Commented Aug 17, 2023 at 10:08