How to Tighten Plumbing Fittings

You can't tighten all plumbing fittings, and those you can tighten almost always have threads. The types of fittings you can't tighten are soldered copper fittings and glued plastic ones. In a typical household, you will most commonly find threaded fittings on the drainpipes under the sinks and on the water supply connections under the sinks, behind the toilet, in the basement and outside. Whether they are on plastic, copper, brass or steel water, waste or gas lines, threaded fittings create a better seal if you wrap plumbing tape around the threads before you tighten them.

You can hand-tighten some plumbing fittings.
  1. Tighten the fittings around the P-trap assembly under a sink by hand. Hold the pipe under the fitting with one hand and screw the nut on the fitting clockwise to tighten it. If the fitting still leaks after you have tightened it as much as you can by hand, tighten it a little further with slip-lock pliers. Don't over-tighten it, or you may strip the threads or crack the nut.
  2. Use a wrench or a pair of slip-lock pliers to tighten the compression fittings on angle stops, which are the shut-off valves connected to toilet and faucet water supply lines. If the fitting is leaking, turn the nut clockwise until the leaking stops. If you can't stop a compression fitting from leaking, turn off the valve and unscrew the nut. Wrap plumbing tape clockwise around the threads on the male part of the connection, then screw the nut back on and tighten it with the wrench or slip-lock pliers.
  3. Stop water or gas leaks from a fitting such as a union or valve that is connected to a length of pipe by using two pipe wrenches. Hold the pipe firmly with one wrench to prevent it from moving, and turn the fitting clockwise with the other wrench. If you can't stop the fitting from leaking, turn off the gas or the water, remove the fitting and wrap plumbing tape around the threads of the male part of the connection before attempting to tighten it any more.

Things You Will Need

  • Slip-lock pliers
  • Plumbing tape
  • 2 pipe wrenches


  • You can use pipe thread compound in place of plumbing tape. It is a thick paste that fills the threads to prevent water from seeping through them. It comes in a tube or a can that has an application brush attached to the lid.
  • The only way to tighten a leaking glue or solder joint is to cut out the fitting and reassemble the pipes with new fittings.


  • Don't over-tighten any fitting. If you have sealed the threads and can't stop the leak by applying reasonable force, it's better to remove the fitting and replace it with a fresh one than it is to risk stripping the threads or cracking the fitting.

About the Author

Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.

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