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Step 1
Clear the kitchen cabinet under the sink first. Remove everything stored in the cabinet so you have room to work. Turn off the water supply to the kitchen pipes, usually located under the sink. If there is no turn-off valve, you may have to turn off the water to the whole house while doing the pipe repair. Remove the kitchen cabinet doors if possible; this allows more room for you to work. Place a bright flashlight or portable light source under the cabinet so you can easily see your work.
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Step 2
Cut the copper pipe with a pipe cutter. The hot water pipe is most likely a 5/8-inch pipe unless you have an older home. That means the outside diameter of the pipe is 5/8 of an inch while the inside of the pipe is 1/2 inch. Measure the length of pipe you need and mark it with a marker. Place the pipe cutter at your mark and twist the cutter around the pipe. Tighten the cutter as you move it around the pipe to get a uniform cut. It's not recommended that you use a hacksaw; a hacksaw can leave burrs on the edge, which can cause your kitchen pipe to leak.
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Step 3
Slide a universal compression fitting over the pipe; it has the compression sleeve attached to the nut. It will be a tight fit, but lightly tap it down until it slides in as far as it will go. Slide the grooved fitting down as far as it will go onto the pipe, then pull the sleeve back up to the fitting and tighten it (this procedure is similar to attaching a hose bib). Make sure you tighten it with a wrench, but don't tighten it so much that you can't turn it. If the fitting is too tight, it can cut the pipe and cause leaks under the kitchen sink.
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Step 4
Install a two-outlet valve on the copper pipe. One outlet is for the kitchen sink, the other is for the dishwasher. Even if you don't have a dishwasher, it's best to install a two-outlet valve for future use. Turn the water on to check for leaks.
