How To Connect Two Faucet Supply Lines Together

With the help of some knowledgeable DIY websites, blog posts, YouTube videos, and big DIY store staff, many plumbing tasks usually performed by licensed plumbers can be tackled by home improvement enthusiasts on their own.  One such task is connecting two faucet supply lines together.

This piece will walk you through enough basic information for you to consider doing this yourself.

We’ll start with the first basic.

Where To Begin Connecting Faucet Supply Lines Together

For tools, you’ll want to have a basin wrench.

A basin wrench is a funny looking, very long handled wrench with a wide mouth used by plumbers to install and remove faucets.  The long handle enables you to reach into spaces that you’d never get to in tight spaces beneath sinks with standard wrenches or pliers. 

You won’t likely need a basin wrench often, but at between $10 and $20, you’ll be glad you spent the money when the time comes to use one. 

The rest of the work in connecting 2 faucet supply lines can be done by hand strength alone, whether you are introducing a fitting known as a sink or pipe nipple or a push-fit plumbing fitting.

The nipple is a short piece of pipe with male threads at both ends used for connecting two other female threaded fittings or pipes.  A push-fit fitting is exactly what the name implies – it is pushed into the ends of pipes needing to be connected. 

A ring of metal spurs grab hold of the pipe end into which they are pushed and are a great way to make pipe connections without having to solder or use clamps or glue. The female threaded end then makes a connection to a male fitting to secure the line.

Hand strength can complete these connections for a tight and uniform supply line without leaks.                   

Making The Connection of Water Supply Lines With Compression Fittings

The easiest way to connect faucet water supply lines together is by using a compression fitting.  Measure your line diameters carefully and purchase the same size compression fitting to join them.

Your local hardware store may very well carry a selection of fittings for this purpose, and certainly, plumbing supply and the big DIY stores will, too.

You connect the water supply lines to the faucet with these fittings.  Standard fittings are the most common types and are typically used for this purpose.  Push-in fittings, though, may also be used, although they are not necessary with copper tubes.

Compression fittings are easy to install, work well where moist pipes prevent soldering and require only periodic maintenance.  However, they are not as durable as soldered fittings and have a slightly higher probability of leaking.  They are, nonetheless, a good choice for the job.

How To Measure For Your Water Supply Line

Beneath the sink, measure from the faucet connection point to the shutoff valve. Then, add three or four inches to that distance to allow for a bit of flexibility and angle, depending on the type of water supply line you are using.

Most faucets come with supply lines, and since you paid for them, be sure to use them.  Sometimes, these supply lines won’t fit as they need to, so buy extensions if they are not long enough.

A supply line extension will not affect the water supply to your faucet. 

When you connect the water supply lines to the faucet and the shutoff valve, you may need to use Teflon tape on these supply line connections (also known as plumber’s tape), which is used to lubricate and seal threaded pipe joints.

Hot and cold water lines should be kept approximately 6 inches apart unless the hot water line is insulated. You don’t want the cold water line to pick up heat from the hot water line.

How Tight Should The Water Supply Line Connections Be?

How tight is too tight?  And what if the water supply line is too tight?

Connections should be tight enough to prevent water leaks, of course.  But too tight runs the risk of weakening the connection or the water supply line itself.  The most common directions suggest to hand tighten as far as you can and then use a wrench for one last quarter or half turn.

Now The How – Installing Faucet Supply Lines

The simple steps:

  • Turn the water off.  Gather your work gear – safety goggles and gloves.  Bring your bucket.
  • Drain the lines into the bucket.
  • Determine which line is which – hot and cold.
  • For flexible water supply lines, install your faucet and wrap the threaded end in several layers of Teflon Tape. Screw the threaded end and use a compression fitting to connect it to the wall’s supply line.
  • For inflexible water supply lines like hard plastic or copper tubes, connect using compression fittings. Just position and bend the pipes as needed to line them up. Insert the push fit fittings for plastic lines and connect with the compression fittings.
  • Turn the water supply back on and check for leaks.

If the connections are tight and there are no signs of a leak, you’re done.  Clean up, put your work gear away, and reward yourself with a cold beverage and afternoon nap.

There’s really no excuse for hiring a plumber to accomplish this basic and simple task once you know the tools and fittings needed.

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