I'm going to install a new gas line tonight for our new dryer. The gas line that that does come out of the wall is capped and does not have a shutoff valve. I cannot tell where it comes from therefore I dont know where the shutoff valve is. So what I was planning on doing was turning off the gas for the entire house at the gas meter, running a new pipe up the wall with a shutoff valve and then put a hose from there to the dryer. My question is, how long will it take to drain the gas lines in the house? How long do I need to wait after I turn it off before starting work?