Informational Guide

How To Plumb A Bathroom

Our guide gives you everything you need on bathroom fittings & components so you can learn how to plumb a bathroom DIY.

by Holly Curell

Plumbing has become a lot more accessible for amateurs over the last few years. There are more resources, videos, guides, and information than ever before that can get you up to speed with basic plumbing work. That being said, there are still some homeowners who find the task intimidating and don’t know where to start.  

This guide will give you everything you need about bathroom fittings, pipes, and connections so you learn how to plumb a bathroom yourself with confidence.  We also recommend getting prices from local plumbers in your area. You can find some free quotes by using the form below.

You want to do your plumbing the right way, and there are a few key aspects you need to consider carefully before starting any work.  

  • Pipe Placement 
    The placement of your pipes, or the intended placement of your pipes, will impact the work you need to do. If you put pipes on an exterior wall, then they'll be influenced by the outside climate and more prone to freezing if you live in a cold area. These types of pipes will need extra insulation, and that means extra work for you. Our recommendation would be to avoid putting pipes on an exterior wall if at all possible.  
  • Water Access 
    Your pipes need to be connected to your water and drainage system, so you need to consider the water access. Organizing your bathroom so that your fixtures are nearer the water supply will make it easier to plumb.  
  • Placement Of Your Toilet Tank 
    Your toilet is obviously a key part of your bathroom, and the plumbing needs to be considered carefully. If you're going for a mounted toilet tank, then you'll need to have a hidden drainage system in the wall. This is more complicated and will take careful planning.  
  • Choosing Your Drain Size 
    The drain is vital to a healthy plumbing system. Your typical drain will be 1 ½ inches which is good enough for most fixtures. However, you may opt for a 2 inch drain which is more efficient and less likely to get blocked. This will cost slightly more, but if you’re plumbing a bathroom for the first time, it's worth doing it now rather than down the line.  
  • Shower Floor Drain 
    Your shower is another vital part of your bathroom. Having a tiled shower floor drain is really popular but takes some careful planning. You’ll need to angle the slope of the tiles to encourage the water to flow into the drain; otherwise, it will end up pooling. Make sure you’re aware of the work involved before you start. 
Considerations When Plumbing A Bathroom

Rough-In & Plumbing of Bathroom Components  

Rough-in’ may not be a term you’ve heard of before, but it's absolutely vital for plumbing. This is the stage of the process where you’ve removed the floorboards, drilled your holes, measured everything out, but you haven't connected up all the pipes and connections. This is your last chance to review everything and make sure everything is correct.  

For the rough-in stage, you’ll want to measure up all the fixtures and fittings. There are two key terms you’ll need to understand: 

  • Centerline
    this is the vertical line the drain takes as it passes through your wall or floorboards
  • Base Floor Height
    this is the height of different fixtures in your bathroom from the floor of the room

Here’s a rough-in guide to all your key bathroom items. 

1. Bathroom Toilets 

Bathroom Toilet Rough-In Dimensions: 

  • Supply Line (Height) 
    8 ¼ inches from the floor 
  • Supply Line (Horizontal) 
    No more than 6 inches from the centerline (a vertical line running down the middle of the toilet) 
  • Discharge Hole From Back Wall Discharge Hole (Vertical) 
    12 ½ inches from the back wall 
  • Drain Located At Floor Heigh
    This should be at floor height and definitely no higher 
  • Fixture (Side To Side Buffer) 
    Keep at least 15 inches free on each side. If you have space, then 18-20 inches is better. 
  • Fixture (Front Buffer) 
    Keep at least 21 inches free in front of the toilet. Again, if you have space, then 30 inches is better. 

How To Plumb A bathroom toilet (Step By Step Instructions) 

  • 1
    Turn Off Your Water Supply 
    Use your shut-off valve to stop any water flowing to your toilet so you can plumb it safely.  
  • 2
    Install The flange 
    If installing a new toilet, you'll need to install your flange in the floor. This is what connects directly to your drain. You’ll just need to slot this on the top of the drain and tighten all the screws. 
  • 3
    Attach Closet Bolts
    Slip the closet bolts into the flange and slip the washers on top. These should point up towards the ceiling. Place a wax ring on top of the flange. This is what will help secure the toilet in place. 
  • 4
    Install The Toilet 
    Carefully lift the toilet into place, so it rests on the flange with the bolts through the pre-drilled holes. Add washers and nuts and tighten, so it’s held in place.  
  • 5
    Level The Toilet 
    Check to make sure the toilet is level and put washers underneath either side if needed.  
  • 6
    Attach The Supply Line 
    The cold water supply line should fit from the wall into the tank of your toilet. Most standard toilets use a ⅜ inch connector, but you may need a different size.  
  • 7
    Check It Fills 
    Switch your water supply back on and make sure your tank fills up and flushes correctly. You may also choose to caulk around the base of the toilet to keep it all securely in place and water-tight.  
toilet parts

2. Bathroom Sinks  

Bathroom Sink Rough-In Dimensions:

  • Supply Line (Height)  
    Your sink will have two supply lines, one for hot water and one for cold. These should both be 2-3 inches above the drain height. 
  • Supply Lines (Horizontal)  
    Each supply line should be 4 inches from the centerline, one to the right, and one to the left.
  • Discharge Hole (Vertical)  
    This should be 16-20 inches from the floor and in line with the centerline.  
  • Fixture (Side To Side Buffer)  
    Leave 15 inches on either side of the sink or, if possible, leave 20 inches. This should be measured from the centerline.  
  • Fixture (Front Buffer)  
    Leave 21 inches in front of the sink or, if possible, leave 30 inches.  
  • Placement Of Sink 
    Your sink should be 31 inches above the floor. This should be measured from the floor to the rim of the sink.   

How To Plumb bathroom sink (Step by Step Instructions) 

  • 1
    Install Pop-Up Drain 
    This is the drain cover that will allow you to control when water is emptied from the sink. Drop this into the sink and slide a rubber ring on the underside of the drain. Add a nut and tighten everything in place.  
  • 2
    Install Your P-Trap Adapter 
    You should have a piece of pipe sticking out from your wall. Apply some glue to this drain and attach the P-trap adapter. This will allow you to connect the P-trap.  
  • 3
    Attach Your P-Trap 
    P-traps generally come in a kit. Connect the pipes to form the P shape and fix it with a nut. Put a connector ring over the P-trap adapter and slide the P-trap into place. Tighten the connector to fix it. Add the U-shaped piece of pipe and slide the connector ring over and tighten. This should now connect up to the pop-up drain you installed in step 1. Use a wrench to make sure everything is connected correctly.  
  • 4
    Check For Leaks 
    This is a crucial step. Run your water and check for any leaks. Hopefully, it's all working correctly, and your job is done! 
bathroom sink parts

3. Bathroom Shower & Bathtubs  

Shower & Bathtub Rough-In Dimensions:

  • Shower Supply (Vertical) 
    Your shower arm should be about 80 inches from the floor. The shower head itself will be 65-78 inches from the floor.  
  • Tub Supply (Vertical) 
    The bathtub faucet valves should be about 20 inches from the floor. Each faucet should be 4 inches on either side of the centerline.    
  • Discharge Hole From Back Wall 
    This should be in line with your centerline and should be 6-8 inches wide.   
  • Discharge Hole (Vertical) 
    This will be located at floor level.  
  • Fixture (Side To Side Buffer) 
    Leave 18-20 inches to each side of the bathtub.    
  • Fixture (Front Buffer) 
    Leave 18-20 inches in front of the bathtub.  

How To Plumb bathtub 

  • 1
    Turn Off The Water Supply  
    Use the shut-off valve to shut off all water to the bathroom. 
  • 2
    Mark The Outline Of The Bathtub  
    Measure up the outline of the bathtub so you can tell roughly where the entrance will be.  
  • 3
    Fit The Drain Line 
    Run the drain line pipe underneath the bathtub and fit it to the bathtub drain.  
  • 4
    Fit The Supply Lines 
    Run the supply lines underneath the bathtub and through pre-drilled holes in your bathtub. This is where your faucet will sit. Remember, you will have one supply line for hot and one for cold. You may need a mixer so you can control the temperature of the water.  
  • 5
    Install The Bathtub 
    Lift the bathtub into place (you may need a friend to help you) and secure it in place. Use caulk to create a water-resistant seal around the edges of the tub.  
  • 6
    Fit Your Faucet   
    Connect your faucet to your bathtub using bolts. Make sure the supply lines are fitted securely to each side of your faucet.  
  • 7
    Install The Shower 
    Connect the pipe from your faucet up about 60 inches from the faucet. Ensure this is connected securely to the faucet and held in place with a clamp or hold it halfway up the wall.  
  • 8
    Connect The Showerhead 
    Connect the showerhead to the shower pipe.  
  • 9
    Test The System 
    Turn the water bath on and make sure it’s all connected and working without any leaks.  
shower parts

Not convinced that you want to do this all yourself? Get a free quote below.

The DWV System (Drain, Waste & Vent) For Plumbing Bathrooms  

The DWV, or drain, waste & vent, plumbing system is used in most modern bathrooms. It’s an efficient plumbing system that allows you to keep even air pressure in your plumbing system. This allows all waste to flow freely through the pipes and drain more easily.  

Basement Bathrooms 

Plumbing a basement bathroom isn’t an easy job. It will often involve breaking through concrete and taking on heavy-duty work to make it a success. For this work, you’ll need: 

  • Screwdriver 
  • Drill
  • Hammer and sledgehammer  
  • Tape measure  
  • Trowel  
  • Masking Tape 
  • Spade  
  • Step ladder 
  • Concrete 
  • Pipe glue 
  • Plastic pipes and fittings 
  • Cast iron pipes and fittings 

Here are the steps you need to take: 

  • 1
    Locate The Main Stack 
    The main stack is the main drain pipe that runs down into the basement. This is typically 3-4 inches wide, and you'll need to look for a cleanout plug on the exterior wall. You’ll need to break through the concrete in the floor to make sure it’s there.  
  • 2
    Plan Your System 
    Plan out your bathroom system on the floor, including all the different fixtures and the drain lines. Draw these on the floor and use masking tape to mark them out.  
  • 3
    Trench The Floor  
    Use a sledgehammer to start breaking through the floor along the main drain line. Remove the larger pieces of concrete and keep the dirt to refill the hole later on in the process.  
  • 4
    Break Open A Section Of Drain 
    You’ll need to open up the main drain so you can install a Y fitting. This will allow you to connect your bathroom fittings to the drain supply.  
  • 5
    Build Your Drain System  
    You’ll need to start building out your drain system for each of your fixtures. Break open the floor and lay the drain pipes to the toilet, shower, sink, and bathtub as needed. Put caps on the pipes as you go, so none of the sewage gas escapes into the basement.  
  • 6
    Seal The Floor 
    With your drains fitted, you can seal up the floor. Put the dirt back into the holes and lay fresh concrete over the patches. Make sure everything has dried before moving to the next step.  
  • 7
    Build Your Vent System  
    Your vent lines should align to your bathroom walls and sit along your ceiling. Assemble the vent lines and connect them into an existing vent using a T or Y fitting, which should be cut into your venting system.  
  • 8
    Position Your Shower Drain 
    Your shower drain will need to be lower than the others in the floor and sloped at ¼ inch per foot. Set the shower pan and drain in place before installing all the different components and sealing everything up. You should now have a fully fitted DWV plumbed bathroom in your basement that works perfectly.  

New Bathroom (with Existing Plumbing) 

Upgrading your existing plumbing to make it more modern and effective isn’t as difficult, but will still require some work. To fit the DWV system, you’ll need to add a few different parts to your fittings. 

You’ll then need to follow these steps: 

  • 1
    Vent The Toilet 
    Your toilet should ideally fit to your main stack, but you'll need it within 6 feet of this for it to work. The best way to vent the toilet is to connect it to the sink drain so it can operate as a wet vent. You’ll need to make sure the toilet is less than 6 feet from the sink for this to work.  
  • 2
    Connect Your Fixture Drainage 
    Your bathtub, sink and shower all need to connect to your waste and venting system. They all need to plumb into your sewage system and the main vent stack. The easiest way to do this is to connect all of your plumbing into one central pipe. This should be located higher than all the fixtures and then attach to your main vent. Your drains can remain separate or joined up.  Ensure that all drainage is sloped at ¼ inch per foot towards the drain outlet, and the vent slopes up ¼ inch per foot away from the drain.  
  • 3
    Replace The Pipes 
    While you’re thinking about re-plumbing your pipes, you should consider the type of pipe you use. PEX is the modern alternative that works well for DIYers because it’s affordable, durable, and really flexible. These are the most straightforward to use, and you should look to replace all the different copper or galvanized metal pipes with PEX if possible.  
toilet pipe

People Also Ask (FAQs)

Is it hard to move the existing plumbing in a bathroom? 

Yes, relocating your plumbing is arduous work and needs careful planning. You should allow at least a few weeks to complete the work.  

Can you use a pex pipe in bathroom plumbing? 

Yes, PEX is a more modern type of pipe that is more affordable and extremely durable.  

Can a toilet and shower share the same drain? 

Yes, though you need to be careful to make sure they have different waste trap arms.  

How many bends can you have in a drainpipe? 

Having more than one 90 degree bend in your drain pipe can cause blockages and other issues, so it isn't recommended.  

Does a P trap have to be directly below the drain? 

Having a P-trap directly below your drain can cause issues because gravity can force the water straight through the drain. It’s typically better to have them at a slight angle.  

Can a plumbing vent run horizontally? 

Yes, as long as it is sloped correctly so it won’t become plugged with water.  


Conclusion

Plumbing a bathroom sounds challenging, but it’s really not. You need to consider your drainage and venting systems and plan them out clearly from the start. This will then allow you to consider each fixture one by one and get them right.  

Hopefully, this article has given you the information you need to get started with confidence.  

Holly Curell is the editor extraordinaire for Plumbing Lab. Having grown up in Michigan, Holly has spent time living in New York, Virginia, & currently North Carolina, where she lives with her husband & family. Holly loves DIY & has years of experience with at-home plumbing problems that arise from having 3 kids & living in colder climates. When she's not writing about her plumbing knowledge, Holly enjoys reading, hiking & relaxing with family.

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