How to Plumb a Sink: The Do’s and Don’ts

plumber fixing something under the sink

Installing a new sink can be a beautiful addition to any bathroom, kitchen, mudroom, laundry room, and more. However, if it is not installed properly, or if it is not installed using the proper steps, it can quickly turn your project into a hassle. Therefore, before installing a new sink, there are few expert tips to consider in order to help ensure your project runs smoothly and the sink works efficiently. Follow our expert tips on the do’s and don’ts of how to plumb a sink.

1. Don’t: Install the Sink First

When installing a new sink, there is a common misconception that the sink can be installed before the piping, and then simply run the piping through the floor to the existing pipe system. However, this is simply not true because sinks not only require drain pipes, which slope downward and into the stack, but they also require vent pipes, which extend upward and join the stack higher on the line, usually in the attic.

2. Do: Open the Wall from the Crawl Space to the Attic

Before you begin your pipework, you need to open the wall from the crawl space up to the attic. Once the wall is open, simply tie the new pipes into the existing drain system in the crawlspace, and then run them up to the sink area, and then to the attic where they will tie into the vent piping system.

Be sure to apply a thread lubricant on all treads to fill the gap between the thread joints to help make them pressure proof and leak proof. You should also be sure to add drain clean-outs where applicable to help make it easier to clear clogs.

3. Do: Consider PEX Piping to Connect the Hot and Cold Water Lines

Though you can use sturdy copper pipes or even CPVC pipes to connect to the main water line in the crawl space, PEX piping, which many professional plumbers often prefer, helps make your job a bit easier because it is flexible and great for long runs. It is also less expensive and easier to fit than both copper and CPVC pipes.

Connect the PEX pipes to the main hot and cold water lines, and then run the piping up the floor and then into the sink area via a pair of drilled holes, 3/4-inch holes for 1/2-inch piping and 1-inch holes for 3/4-inch piping, on the wall or floor near the sink.

When using PEX piping, be sure to fit the main water pipes with PEX adapters, and then solder them before connecting the flex tubes to the adapters for a sturdier fit.

Connect the handles and the faucet to the sink. Afterward, run the PEX pipes to the sink handles using hard lateral rises, which are available in chrome and copper. Secure the hard lateral rises to the handles with nuts. Be sure to secure the base of the PEX pipes with grommet rings.

4. Don’t: Use Plastic Drain Pipes

Though plastic drain pipes, such as polyvinyl chloride (PVC) and polyethylene (PE), are a common choice for many plumbing projects due to their low cost, many professional plumbers recommend using metal pipes when possible because they are more durable and last a long time.

Assemble the top half of the drain pipe system together, and use adhesive on all threads to help secure it. Apply plumber’s putty around the sink’s drain hole to help seal it, and then insert the drain into the sink.

Connect the top of the drain pipe system to the sink’s drain hole and the linkage to the faucet if you are installing a bathroom sink.

Finally, connect the remaining drain pipes, including the P-trap, to the sink to complete the installation.

5. Do: Use Sealant on all Threaded Plumbing Connections

Applying a sealant, such as pipe dope or Teflon tape, to all threaded plumbing connections helps provide a watertight seal, so keep this in mind when connecting and installing the drain pipes.

6. Do: Use Lead-Free Solder

Should you choose to run copper lines or tie into copper lines for your project, be sure to use lead-free solder for any water that may enter the body.

When soldering joints, consider using a soldering flux on pipe fittings. It helps ensure the solder gets way down into the fitting as opposed to just remaining on the surface. This helps ensure the joints are filled with solder and properly fitted to prevent leaky joints.

Dry fit the pieces together before soldering to help ensure a proper fit.

7. Do: Check for Leaks After Installation

Once the sink is properly plumbed and installed, turn the water back on, and inspect the sink area for leaks.

Turn on the faucet, and fill the sink with water. If it is a bathroom sink, allow the water to fill past the overflow to be sure the overflow is properly draining.

Next, inspect the floor near the hot and cold water lines to be sure there are no leaks. Inspect the drain pipes and all other attachments for signs of leaking.

Lastly, allow the water to drain from the sink to be sure the sink is draining properly. It should drain pretty quickly.

To maintain your new sink, keep the drain clean, and have a sink plunger on hand to address clogs.

Bottom Line

Overall, how to plumb a sink is pretty straightforward provided you have some understanding before beginning your project. These tips on how to plumb a sink are expert tips that can help you get the most out of your sink installation. If you have used these tips on how to plumb a sink and have found them useful, or if you have experience with how to plumb a sink and would like to share your tips with others, then feel free to share your knowledge.

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