For a while I struggled with ensuring that a joint between two metal plumbing fittings did not leak. On my most recent project that required multiple threaded fittings I took some time, did my research, and finally sorted out the details.
There are four things to do that will ensure a water tight joint:
- Join like metals together: Use the same, or similar, metal types for both male and female fittings. If you have copper pipe, use a copper or brass fitting. When joining dissimilar types, the threads of the harder metal can distort or destroy those of the softer metal and will result in a leak.
- Use professional teflon tape: Do not use the cheapo, thin tape that you get at the commercial hardware store. Go to a professional plumbing supply store and get a thicker tape that is made for the type of metal you are using. Wrap it 3 or 4 times, and no more. Too much tape can cause it to bunch up and leak. Wrap it on the male threads, clockwise as you are looking directly at the male fitting with it pointed towards you so that when you screw it into the female fitting it continues wrapping the tape tight and not unwinding it. When applying it, unroll a bit of it and hold it to the male threads with your thumb, then wrap it around, pulling it tight into the valleys of the threads, but not too tight that it rips the tape. It is important that the tape is seated into the valleys of the threads.
- Use a good quality pipe dope, and less that you think: Once the tape is applied, coat it with pipe dope. Only fill the valleys of the threads so that the ridges of the threads are still visible.
- Tighten it to that “just right” torque: There is no universal torque spec for all plumbing fittings. Apply the same principle from automotive mechanics; ensure that you do not cross-thread the fitting and then tighten it until it starts to snug up and then tighten it “just a bit more” instead of “as tight as possible”. This is the most difficult part and does require some experience.