If you are capping off a gas line, then you need to take the necessary precautions. Follow the step by step directions below to cap off the line.
Step 1 - Measure the Size Pipe
Depending on the gas line you are looking to cap (a dryer vent for example), you will need to measure the pipe. Measure the diameter and the circumference of the pipe. Look for any markings or ratings on the pipe. Note it on a piece of paper.
Then, you will need to purchase a gas line cap that will fit the measurements. Any home improvement store will sell them. You will also need to purchase a roll of yellow Teflon tape. The yellow Teflon tape is made specifically for this type of application.
Step 2 - Wrap Tubes with Tape
Pull the gas line out and wrap it tightly with the Teflon tape. Submerse the newly wrapped pipe into a very shallow dish or bowl of soapy water. Pull out immediately and inspect for bubbles. If you see signs of bubbles, then you have a leak and you need to add additional Teflon tape.
Step 3 - Add Cap
Insert the gas cap over the Teflon tape. Screw it on tightly. Test it again for leaks and repeat the process if necessary.