How To Plumb a Bathroom (with multiple plumbing diagrams)

The Toilet

The toilet is arguably the most important part of a bathroom, and it has special waste and venting requirements. Ideally, it should be directly connected to the main soil stack, which is the vertical pipe that runs to the sewer. If it has a 3-inch outlet, however, it must be located within 6 feet of the stack for this to be possible. The most common way to work around this is to connect the toilet waste line to a sink drain, and allow that drain to function as a wet vent. In this case, the sink must be within 6 feet of the toilet.

When Should I Use a Y?

  • In the drain system, use a Y-fitting to connect horizontal pipes (Photo 3). Along with a 45-degree “street” fitting, you can use a Y-fitting to run vertical drainpipes into horizontal pipes as shown. A Y-fitting can also be used in vent systems.


In cold weather climates, plumbing vents need to be increased in size before extending out through the roof

This increase prevents the vent from closing due to frost (IPC 903.2)(UPC 906.7). Check your local code for the appropriate size but usually, it’s 3 inches. This increase should also be made within the building’s thermal envelope. Or in other words, within the heated portion of your home. Again check your local code.

So that wraps us this article.

And maybe your wondering:

Getting a Handle on Bathroom Plumbing

The following sections show how to install the three major bathroom plumbing fixtures in a common configuration. You'll even find some variations on this basic arrangement. Your situation may call for pipe runs that differ from those shown, so you may need to develop a unique plan that suits your home.

You'll need a good understanding of the basic skills and techniques of plumbing. Pay special attention to the drain vents, and make sure you use pipe types and sizes that conform to code. If possible, hire a professional plumber to spend an hour or two giving you advice. This modest investment could save you time and money later.

Whether you are remodeling an existing bathroom or installing one in a new addition, you will need carpentry skills. Modifying framing sometimes can make the plumbing work easier. Plan and install the plumbing so it does as little damage as possible to joists and studs; reinforce any framing members that have been compromised. It's usually best to run any electrical lines after the plumbing has been installed.

What’s the Vent For?

  • A plumbing vent is kind of like the air intake on a gas can; it lets in air.
  • Without venting, a slug of sewage racing through a waste line creates air pressure and vacuum in the pipe. That means noisy, gurgling drains. Even worse, the vacuum can suck all the water out of traps, allowing sewer gas to flow freely into your home. Yuck.

Preparing the Site

You can't turn just any spare room or large closet into a bathroom. Whether you are framing a new space or remodeling an existing one, make sure the framing accommodates a bathroom's needs. Remove drywall or plaster from the areas where you will run plumbing. Clear out all cabinets, fixtures, and other obstructions. Check out our handy tips for everything you need to know.

Project details


1 out of 5 Easy You’ll need to solder one joint for a new installation, but the rest of the job is a breeze.

To add a plumbing cleanout, you’ll need two additional fittings:

A 3” cleanout adapter…

And a 3” cleanout plug…

The cleanout adapter glues right into the inlet of the combo. And provides a convenient point of access to rod the drain in case of a backup.

By the way, other types of DWV fittings work for vertical to horizontal transitions.For example,

Wye with 45

Long Turn 90

Two 45’s

Let’s move downstream into this drainage system.

In the plumbing diagram below, notice how the bathroom’s 3-inch drain wye’s right into the building drain.

That’s just a 3-inch wye (with 45). You could also use a 3-inch combo for this connection.

Now that you have a good handle on this bathroom’s drainage system,

Let’s switch gears and talk about…

7. Incorporate Lighting in Your Design

You can create a great relaxing ambiance with the right bathroom lighting. LED recessed lights with wall sconces to work well beside or over a mirror. Install dimmer switches if these are too bright.

Well-installed vanity lighting can eliminate shadows from your face when you examine yourself in the mirror. Overhead and ambient lighting, like sunken track lightning or frosted glass fixtures, can also offer a soft and relaxing sheen.

Plan the lighting early and speak to your plumber and contractor about your ideas early on. This ensures that the plumbing and electrical wiring will be safe and work beside one another.

Project Difficulty

The idea of putting in a bathroom can seem simple enough to an experienced DIYer, but many people overlook the complications of having to dig up the concrete foundation in order to run drainage lines at the appropriate angle for efficient waste disposal and to avoid clogs. Running new wires to the bathroom may be within your skill set, but it's also necessary to ensure that the new circuits are connected properly to the main electrical panel, which is a task best left to a master electrician.

Overall, installing a basement bathroom is a project that is best handled by one or more licensed professionals. However, experienced DIYers may want to take on parts of the project to help reduce the overall costs. Some steps that are more DIY-friendly include installing the vanity, putting up drywall, installing the faucets, and even tiling the floors. Just make sure that every stage of the installation follows the appropriate building codes in order to avoid potential problems in the future, like a leaking foundation.

Issues to Consider When Installing a Bathroom Yourself

If you are designing or installing your own new bathroom, there are a few points you will want to keep in mind. First, the bathroom must have ventilation. When choosing your space, try to find one with a window already built-in. If you can’t, you will need to put in a duct fan or a new window of some kind.

Make sure your floor can handle the weight of your new bathroom, as bathroom fixtures can weigh up to 20 pounds per square foot. Find out what kind of capacity your floor joists are equipped to handle.

Do the math. The main reason to do bathroom remodeling yourself rather than call a professional is economic. Between the tools, equipment and supplies you will need to purchase and the amount of time you need to dedicate to the project, you might not actually save that much money. It can be a good idea to get a professional estimate first before even considering taking on bathroom remodeling on your own.

Costs are another factor to consider. While a bathroom can be added very affordable by taking into consideration your current bathroom situation, the average cost to add a bathroom in 2019 is around $7,600. This can be as low as $2,500 if updating an existing space and keeping the upgrades simple, or as high as $25,000 if adding an entire addition onto your home to make room for the new bathroom. Regardless, there are ways to cut costs while still building your dream bathroom. Ask your plumber or contractor about the most cost-effective ways to incorporate your new bathroom.

Central PA fixture installation Services

Plumbing Tips for Adding a Bathroom

When you’re adding a new bathroom, consider these tips to help make your project a success:

  • Know what you want your new bathroom to look like before you start. Check out Pinterest photos and home improvement sites online for ideas.
  • Place fixtures strategically. If you can place your new fixtures close to existing water and waste lines, you can keep construction costs and plumbing bills down.
  • If you’re installing a door in your new bathroom, install one that swings out or a sliding door. This will maximize the available space for fixtures and make it easier for guests to navigate inside your new bathroom.
  • Keep an eye out for products that will make the process easier, either because they are more affordable, easy to install or both. For example, the Qwik Jon® Ultima Sewage System by Zoeller is designed so you can put a toilet just about anywhere, which is perfect for your new bathroom project. However, adding a toilet to an existing bathroom in an old house will be a huge cost saver as it will drastically cut installation time.

Can you add a bathroom anywhere in your house?

The short answer is yes, you can install a bathroom almost anywhere that you can afford it. However, this will largely depend on your plumbing and electrical setup and what style of bathroom you want, which goes into another common question.

Return on Investment

You may already have the budget to dedicate to installing a basement bathroom but are wary about your potential return on investment (ROI). However, this fear is usually unfounded. As long as the bathroom installation is completed according to local building codes with the authorization of a building permit, you can expect a great ROI. This means that when the home sells, you can expect the bathroom to increase the cost of the home by much more than the initial cost of the bathroom installation.

Adding a basement bathroom to a home that currently only has a single bathroom won't just increase the value of the home, but it will also make it much easier to sell the home because most prospective homebuyers are more interested in properties with two or more bathrooms.

3. Keep Your Existing Plumbing in Mind

If you’re installing a new bathroom in your house, such as on the second floor or in a newly renovated basement, you should keep in mind existing plumbing and electrics.

Locating your new bathroom as close as possible to existing plumbing makes it much simpler (and cheaper) to get everything connected.

In the case of a basement bathroom, try to locate the bathroom directly underneath another. You should also keep in mind that an extraction fan will likely be needed. This needs placing on an exterior wall for outdoor venting.

If you’re merely remodeling a bathroom, think about whether the same layout for fixtures will work in your design. Keep in mind that moving pipework will add to the cost and complexity of the project.

Hooking up the plumbing

It’s easier to install the drain and overflow pipes on the tub before it’s permanently installed in the enclosure. Turn the tub over or rest it on its side and then follow these steps:

  1. Follow the manufacturer’s directions and assemble the shoe fitting, which is placed under the tub and the waste pipe.

  2. Assemble the overflow fitting with the overflow pipe.

    Insert the ends of the overflow pipe and waste pip

    Insert the ends of the overflow pipe and waste pipe in the T-fitting.

  3. Put this assembly in place to check that shoe and overflow align with the openings in the tub.

  4. Place a bead of plumber’s putty around the drain flange and wrap Teflon pipe tape around the threads on its body.

  5. Place a rubber washer on the shoe and position the shoe under the tub in alignment with the drain flange.

  6. Screw the drain flange into the shoe.

  7. Tighten the drain flange.

    Place the handles of a pair of pliers in the drain flange. Insert the blade of a large screwdriver between the handles of the pliers and use it as a lever to tighten the drain flange.

  8. Place a rubber washer on the overflow drain and install the overflow cover with the screws provided.

    You may want to leave the drain linkage and pop-up assembly out of the tub until you set it in place.


  • Make sure to wear protective glasses, noise-canceling headphones, and gloves.

    Thanks! Helpful Not Helpful

  • Ask for help moving heavy fixtures.

    Thanks! Helpful Not Helpful


Tools Materials

  • Propane torch

    Propane torch

  • Striker


  • Tubing cutter

    Tubing cutter

  • tubing bender tool

    tubing bender tool

  • Adjustable wrench

    Adjustable wrench

  • Drill/driver


  • Hacksaw


  • Jigsaw


  • Handsaw


  • Level


  • Screwdriver


  • Tape measure

    Tape measure

  • Utility knife

    Utility knife

Water Supply

The supply pipes for the bathroom can be copper, chlorinated polyvinyl chloride, or CPVC, or cross-linked polyethylene, better known as PEX. Polyvinyl chloride, or PVC, pipes aren’t suitable for interior residential plumbing. Each should have a diameter of 1/2 inch and connect to a main 3/4-inch pipe. It’s a mistake to draw water for any bathroom fixture from a 1/2-inch branch line that services another fixture. That creates competition for water and is one of the main reasons a shower suddenly turns cold while you’re using it. The usual practice is to “T” each supply line in at the closest available location on the main pipe. Keep the hot water branch pipes as short as possible to avoid having to wait for hot water.

Common questions about adding a bathroom

Is there existing water and waste piping near your new bathroom?

Before installing, check to make sure that water flow exists for your new bathroom. If it doesn’t, you may need to hire a professional plumber to sort out your needs and get water flow to the room of your choice.

Do you have enough space for a bathroom?

An important question to consider, as not every space can fit all the bathroom necessities you may require. The starting point for most bathrooms is roughly 25 square feet-this size gives you just enough room for a small bathtub, a toilet and a sink, though keep in mind this size may be too small for you.

Does your city code allow you to add a bathroom in your designated space?

Another tricky subject as every city will be different and it is important for you to consult your nearest authority on the matter. Many cities do not permit alterations to your home or some extensions may be too large for city code without the right permits, so it is best to understand what you can and cannot do to your house before you begin.

Should you have a professional assist with adding a bathroom?

The short answer is yes. In many cases, electrical and plumbing alterations must be handled by a trained professional. If you are confident of your abilities and have the requisite experience, then some steps can be DIY, but ultimately, utilities must be handled by a professional.

Adding a bathroom to your home can help to increase the value of your home, but it would be best to consult a professional to assess your situation to prevent any unnecessary building mishaps that may occur and further costs as well.  

Reader Success Stories

  • Anonymous

Jan 3, 2018

    Anonymous Jan 3, 2018

    “Installing a bath fan has been confusing until now. Good article in sequential steps.”

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