We have several ways to detect a leak on a gas line. The first way to detect is through smell, natural gas smells somewhat on the lines of rotten eggs. If you need to investigate further, we advise you to use soap and water in a spray bottle. When you have your soapy concoction made, start by spraying the fittings. These fittings are usually where most leaks start, you will notice the soapy water starting to bubble in the area of the leak.