Using and Choosing Plumbing Compression Fittings

plumbing compression fittings

If you are a homeowner, particularly the kind who doesn't shy away from simple do-it-yourself projects, chances are good that you are going to run into a situation where you need to install plumbing compression fittings. By design, compression fittings were made to simplify life ... or at least plumbing!


Plumbing compression fittings connect a pipe to:

  • another pipe
  • a fixture (like a sink or toilet)
  • or an appliance (such as a dishwasher)

to create a watertight connection. As the examples suggest, the usual places to find these fittings are under sinks, behind toilets and connected to appliances that require a water supply.


Plumbing compression fittings have three parts: a nut, a compression ring and a compression seat. The nut and the ring slide over a tube or pipe. The seat slides onto the other connecting pipe/tube/fitting. When the nut is tightened, it compresses the ring into the seat making a seal.

Pros and Cons

The advantages of using plumbing compression fittings outweigh the disadvantages. They are easy to assemble and easy to take apart, inexpensive, simple enough for any do-it-yourselfer, usually durable for the life of an appliance or fixture (if installed correctly) and easily replaceable if necessary. Since they allow plumbing connections without soldering, plumbing compression fittings are safe in confined areas, like under a sink.

The disadvantage of using plumbing compression fittings is that if they are installed incorrectly or are used in the wrong application, they will leak. They also aren't a strong, soldered finish. There are a few "don'ts" as far as installing plumbing compression fittings go:

  • Don't use if the piping or tubing isn't stationary.
  • Don't use to lengthen pipes (the exception is behind a sink when movement and stress are unlikely).
  • Do not reuse plumbing compression fittings.
  • Don't over-tighten the fitting.
  • Don't move it once tightened (any amount of stress can cause a leak).


While you don't need any particular skill to install compression fittings, you do need a tube cutter. Chances are slim that you are precise enough with a hacksaw to get a cut that will work with the fittings. A tube cutter is easier and more precise. You'll also want to lube the threads of the compression nut before you tighten it, but do not use plumbers' tape or joint compound. Compression creates a watertight connection. The use of tape or joint compound can compromise the seal.

For professional help with piping connections and other plumbing work, find a licensed plumber in your area.

Updated July 4, 2018.

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