How To Plumb A Bathroom Sink (Step By Step Guide)

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DIY is becoming increasingly popular, but people often think that plumbing can be too difficult to attempt yourself. Despite how daunting it might seem, plumbing a bathroom sink yourself can save you a lot of time and money and actually isn’t too challenging.

This guide will give any aspiring plumber all the information you need to successfully fit a bathroom sink and all the different connections.

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How To Plumb Your Bathroom Sink (Step-By-Step Instructions)

Plumbing a Bathroom Sink Drain

The first step is to plumb the sink drain:

1
Attach a female adapter onto the drain stub in the wall. This can typically be done by hand.
2
Attach some slip nuts onto the drain arm and the sink tailpiece and connect them into the drain stub. This is how your water will eventually drain into your pipes, and your P trap will connect into this.
3
Once these are all in place, then use a wrench to tighten the nuts.
4
Carefully check that everything is completely secured.

Plumbing a Bathroom Sink P Trap

Once you’ve plumbed the drain, you can attach the P trap into the sink:

1
Slide the P-trap onto the sink tailpiece and move the P-trap up or down as needed so that it’s higher than the hole in the wall. If you need to trim it down further, you can use a hacksaw.
2
Now, take the lower part of the P-trap and slide it into the drain. Pull the trap arm out and align it with the U-shaped top.
3
Thread two nuts onto the P trap and make sure everything is aligned correctly before tightening with a wrench.

Plumbing a Bathroom Vanity Sink Drain

1
Turn off your water valves
2
Measure your pipes and cut out corresponding holes in the back of the vanity cabinet
3
Remove the doors from the vanity cabinet to make the plumbing work easier
4
Slide the vanity cabinet into position. Use a drill to secure it to the wall
5
Install your faucet and the P-trap using the steps above
6
Use plumbers putty underneath the ring of the sink drain to secure it in place
7
Connect the supply pipes and switch the water valves back on

Plumbing a bathroom sink with PEX

PEX (short for cross-linked polyurethane) is modern plastic piping that is much cheaper and quicker to install than traditional copper pipes. It has more flexibility and can bend as needed to fit. PEX is used for the supply lines, and you can plumb a bathroom sink with it by following these steps:

1
Cut the PEX to the right length and make sure the cut is straight to avoid leaks
2
Attach crimp fittings to each end of the PEX pipe. Attach one end to the faucet and compress it, so it fits tightly. Attach the other end to the cut-off valve.
3
Tighten the nuts on the ends of the PEX piping. PEX comes in a range of different colors, so it might be worth using two different colors for the hot and cold supply.
4
Turn on the water and check for any leaks.

Plumbing a Double Sink Bathroom Vanity

A complete guide to plumbing a double vanity bathroom sink can be found here.

Important Parts to Bathroom Sink Plumbing

Before you can install a bathroom sink, you need to understand all the different parts just like professional plumbers would learn. Here’s a quick breakdown:

Shut-Off Valves

Shut-off valves are small valves that control the flow of water into your sink. You’ll have two supply tubes coming into your bathroom for the sink, one for hot water and one for cold water. Each of these will have a shut off valve which allows you to stop the flow of water for each without having to shut off the whole water supply for your home.

Supply Tubes

Water supply tubes are connected to your faucet and a shut off valve with compression nuts. There’s one for hot water and one for cold water, and they supply the water for your sink. These supply tubes are typically made from copper, plastic (PEX), or a metal mesh.

Drain Tailpiece

The drain tailpiece is what connects the bottom of your sink to the drain, and it's literally where your water will drain to. These are usually attached with a nut and a washer and should connect to the port at the back of the sink.

P-Trap

The P-trap is made up of two parts: the u-bend and the trap arm. The p-trap connects your sink to the sewage line while preventing any gas from rising back out of the sink. The u-bend is filled with water which helps stop the bad smell coming back up out of your sink, and when you run the sink, it flows out into your pipes and replaces the water in your u-bend.

Drainpipe

The drainpipe is what connects your sink to your plumbing system. These are usually a set size, 1.5 inches in diameter, and connect to the trap arm with a nut.

Considerations Before Installing or Replacing a Bathroom Sink

Configuration

The configuration of the bathroom sink is just the type of sink you have. Some sinks have a single hole faucet, while others have three holes. You’ll need to be aware of the specific configuration to understand how the plumbing will work.

Bathroom Size

The size of your bathroom will directly impact the type of sink you can install. Bathroom sinks with no base can work well in smaller bathrooms or wall mounted models. These will be slightly more complicated to plumb in though.

Traffic & Lifestyle

The type of sink you choose to install will be influenced massively by the amount of use it will see. A busy home will need a very sturdy and durable sink, but a more stylish, less hardy unit may work in an en suite that sees less use.

Storage Needs

You need to consider the storage options when selecting a sink. A busy bathroom with a lot of users is likely to have a lot of different products in there, and you might need to consider a vanity mounted sink, which gives more storage space.

Maintenance Requirements

Every sink is different, and some need more maintenance than others. You’ll need to decide if your preference is style or durability because often, the more durable ceramic sinks are less aesthetic. Consider how often you’re prepared to undertake maintenance on the sink before settling on the one you want.

Bathroom Sink Rough-In Guidelines

Rough-in is the term used for when the electrical or plumbing work is done before your wall is sealed up.

There is still some wiggle room to make amendments, but it isn’t the end of the world if your measurements aren’t quite right. That being said, you’ll also want to get this as close as possible so you can plumb the sink properly.

Note that you will need to understand the term ‘centerline’ for this. The centerline refers to an imaginary line drawn down the center of your sink. This should line up to your drain.

Supply Line (Height)
Your supply line-height should be roughly 2-3 inches higher than your drain pipe. Remember, you’ll need two of these.
Supply Lines (Horizontal)
You’ll need two holes here as well. One should be 4 inches to the left of the centerline and the other 4 inches to the right.
Discharge Hole (Vertical)
The discharge hole should be 16-20 inches from the floor and in line with the drain (or centerline).
Fixture (Side To Side Buffer)
The side-to-side buffer should be at least 15 inches but aim for 20 inches if possible.
Fixture (Front Buffer)
The nearest obstruction in front of the sink should be more than 30 inches away if at all possible. The absolute minimum is 21 inches.
Placement of Sink
The sink should be 30-33 inches from the floor. This is the measurement from the floor to the rim of the sink.

Professional Plumbing Quote

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FAQs

Which is easier to plumb, a new sink or a second-hand sink?

A new sink is generally easier to plumb because you know everything is working. A second hand sink may be damaged, which makes the plumbing a bit more challenging.

Do I need Plumbers Putty for the bathroom sink drain?

Plumber’s Putty isn’t necessary for more bathroom sink drains but can be useful to secure the drain in place.

When should you not use Plumbers Putty?

Plumbers putty shouldn’t be used when you need a strong adhesive. It also isn’t watertight, so don't use it to create a seal.

Which is better for leaks: Teflon tape or plumbers putty?

Teflon tape will help stop a leaking pipe that’s under strain. Plumber's Putty will provide some water resistance but won’t withstand significant pressure. Teflon tape is, therefore, better for leaks

Can a sink drain go straight down?

A sink drain can go straight down, but it isn’t recommended. The U-bend in the pipe is important because it allows the water to drain through your plumbing without any of the gas from the sewer traveling back up through your pipe, causing a bad smell.

Conclusion

Plumbing a bathroom sink seems scary at first, but it’s actually not too challenging. Hopefully this guide has given you clear guidance on how to plumb a bathroom sink and given you confidence that you can do this without a professional.

Ian Haynes

Ian Haynes is an expert writer who has successfully deployed over 500 plumbing pages and other related content. He has an excellent understanding of home plumbing issues and translates his experiences via Plumbing Lab so readers can have a better understanding of common household problems. Outside of his work, Ian likes exploring Brooklyn with his Labrador.