Informational Guide

How To Plumb A Toilet & Drain

We show you everything you need to know about how to plumb a toilet DIY, saving you a fortune on plumbers.

by Ian Haynes

DIY is extremely rewarding. It’s great to create, build, or install something with your own hands, and it's a brilliant way to save money. Unfortunately, many people think that plumbing is too challenging, and they won’t dare to attempt plumbing their bathroom.  

DIY plumbing is actually much easier than people think, and there's a wide range of resources available online to help you along the way. This guide will tell you everything you need to know so you can install your toilet and connect all the pipes and fittings.  

Before you start work, you need to understand a toilet. There are two main parts to a toilet, the tank and the bowl, and each has its own purpose. 

  • Bowl
    the bowl holds the water which your waste will go into. It connects to the drain and, when flushed, the drain opens allows the water to flow down with the waste and leave your home. 
  • Tank
    the tank holds the mechanisms for the toilet, which allow it to flush and refill. The water reserve is kept in the tank, and this will be refilled by the supply line every time you flush.  

Both of these elements work in tandem seamlessly so you can use your toilet every time. The diagram below gives some detail of the different components.  

How To Plumb A Toilet

Things to Understand Before Plumbing A Toilet  

Plumbing your toilet isn’t something you should just jump straight into. There are some different things you need to understand that will help you plumb effectively: 

Toilet Drain Size 

Toilet drains are pretty much always the same size, 3 inches. You’ll never have a drain smaller than 3 inches in diameter, but you may get some that are larger. The drain size will determine how much water goes through your system and the drainage fixture unit (DFU). All drainpipes can only have a certain number of DFUs, but if you have a 4-inch drain with a 3 inch horizontal drain, you can help improve the flow of water, improving your overall drainage.  

How To Plumb A Toilet Drain

Toilet Vent Size 

Every toilet has to have a vent to help regulate the pressure of the water. The plumber's code determines your vent size, but it's typically no less than 50% of the drain size. This means most vents are 1.5 or 2 inches.  

Toilet Trap Arm Length 

The toilet’s trap arm is the pipe between the drain and the trap. There’s no regulatory limit on the length, but it should be less than 6 feet. The trap is an important part of your plumbing that keeps your wastewater flowing while preventing any sewage gases from rising up through the pipes.  


How To Plumb A Toilet (Easy DIY Guide) 

To plumb a toilet successfully, you’ll need some tools and materials: 

  • Wrenches 
  • Screwdriver 
  • Silicone 
  • Adjustable pliers 
  • Pipe Cutter or Hacksaw 
  • Pipe Wrench 
  • Box Spanner 
  • Hammer 
  • Spirit Level 
  • Drill 
  • Tape Measure 
  • Pencil 
  • Bucket 
  • Towel 

Here’s a step-by-step guide to three common scenarios. 

Plumbing a Toilet in a Concrete Slab 

Typically, a toilet is installed before your concrete slap because your drains would sit below the poured concrete. However, if you already have a concrete slab it is still possible to plumb your toilet:  

  • 1
    Locate the stub out 
    Your flange, or toilet flange, will connect through your floor into your drain. You’ll need to install this before you can fit your toilet or any accompanying plumbing. Locate your stub out in the concrete, which is where your drainpipe comes out of the floor. First, you should place your flange on the floor with the rubber facing upwards. Ensure the screws align to where your toilet base will be and mark down the drilled holes on the floor.  
  • 2
    Drill the holes 
    Using your rotary hammer and drill bits, make a 1 ½ inch hole in the concrete at each of the four marks. Make sure you wear eye protection throughout this step.  
  • 3
    Secure the anchors 
    Put anchors into each of the four holes. Hammer these into place (gently) and make sure they’re secure.  
  • 4
    Place the flange 
    Apply lubricant to the flange and push this down onto the anchors, so they go into the four pre-drilled holes. Push down until the lower end of the flange sleeve is starting to cover the stub up.  
  • 5
    Secure the flange 
    Use a wooden block and hammer to secure the flange on top of the stub, so it fits snugly. Install 4 bolts around the outside and tighten with a ratchet.  
  • 6
    Slide the bolts in 
    Slide the head of 2 bolts into the flange so they’re pointing upwards. This is what your toilet will eventually connect into. Put a washer over each bolt. 
  • 7
    Install the wax ring 
    Slide a wax ring on top of the flange with the waxed side facing upwards.  
  • 8
    Set the toilet  
    Lift the toilet and carefully set it on top of the wax ring on the flange. You should ask a friend to help you with this because it can be tricky on your own.  
  • 9
    Adjust and secure 
    Adjust the toilet so the tank is sitting against the back wall. When in place, put a washer and a nut on each of the bolts pointing upwards into the toilet and secure in place. Make sure this is done securely and that the toilet doesn’t wobble.  
  • 10
    Attach the supply line 
    Take one end of the 16-inch supply line and screw it into the back of the toilet tank. This will allow cold water to flow into the toilet so that it can operate correctly. Screw the other end of the supply line into the shut-off valve located in the wall.  
  • 11
    Test the toilet 
    Turn the water supply on and see if the water is flowing correctly. If there are any leaks, then turn the water back off and fix the issue.

A full guide to plumbing a toilet in a concrete slab can be found here:  


Plumbing a Toilet Waste Pipe & Toilet Drain 

It’s important to get your ventilation and drainage right when installing your toilet, and you'll need to be precise. Here are the steps you must follow: 

1. Choose your ventilation 

There are three different options for vents: 

  • Parallel Connections
    If your venting wall is parallel to the drain, use a Y connection and an elbow pipe to point in that direction. 
  • Indirect Connection
    If your drain line doesn’t connect to a vent, then you'll need to redirect it. Use Y connections and elbow drains to direct it towards a vent line. 
  • Opposite Side Connection
    If your venting wall is opposite, then use a Y connection and pipe to direct it towards that call. 

The choice you make here will determine the materials you need.  

2. Align your drain 

Fit a 3-inch-wide pipe into your drain, and then install a Y fitting into this. This will allow you to direct the drainage and the venting in different directions. 

3. Insert the assembly  

Insert the assembly through your wall plates and anchor it in place. Once you’re content with the positioning, then use glue to hold it in place.  

4. Run your horizontal pipes 

Lay the pipes horizontally so they can connect to your toilet. Make sure the pipes are sloped ¼ inch per foot so wastewater will flow easily.  

5. Run your vent pipes  

Run ventilation pipes up vertically to the ceiling. These will allow any harmful sewer gases to be contained in the system.  

How To Install Plumbing For A Toilet

6. Check all fittings  

Make sure that your wastewater is draining correctly and no gases are escaping into your home.  


Plumbing a Wall Mounted Toilet 

1. Assemble the frame 

Assemble vertical frame bars and horizontal support bars, and secure them together. Secure the fixing mounts to the cistern, and attach the vertical flush pipe to the bottom of the cistern.  

Use the frame to support the cistern and attach an elbow pipe to the bottom of the flush pipe. Clip the feet into the lower part of the frame and install the clamp for the waste pipe into the elbow.  

How To Plumb Wall Mounted Toilet

2. Measure and mark 

Draw a line down where the drain goes in your wall and mark at 1m from the floor and 1.08m from the floor. This will set your toilet at 40cm from the floor, which is standard. Make a mark at 235mm on either side of the vertical drain line.  

How To Do Plumbing For A Toilet

3. Complete the assembly  

Attach the 90-degree waste pipe to complete the assembly of the unit. This should attach into the elbow fitted in step 1. Attach this waste pipe into your floor drain and make sure the whole unit is at least 230mm from the wall.  

4. Attach the unit 

Drill 10mm holes in the wall and insert the rawl plugs. Drill 12mm holes in the floor and insert more rawl plugs. Adjust the height of the frame so that it lines up with your mark AWhen it aligns, secure the feet of the frame into the hole.  

Attach the fixing brackets to the top of the frame and use a wrench to secure them tightly. Attach the waste pipe using the clip that was attached in step 1.  

5. Install the flush mechanism 

Remove the cover and attach the exterior portion of the shut-off valve to the cold water supply. Connect the interior water inlet to the valve, too, so water can flow through it. Connect the other end of the inlet hose to the flush mechanism within the device.  

6. Cover the unit 

Cut holes in the covering panel to correspond with the unit’s opening and side, and cut holes for the waste pipe and the flush pipe. Attach all of these panels around the unit.  

7. Install the bowl 

Place the flush pipe on the bowl and mark where they extend past the bowl. Then place them in the holes in the wall and mark where they emerge from the unit. Use a file to shorten the pipes to meet these measurements and insert the pipes into the unit.

Screw threaded rods into the exterior of the frame and place the bowl over these. Place a washer and nut over the bolt and secure in place. Make sure the bowl is level before moving on.  

8. Install the toilet controls  

Cut out the mounting bracket for the flush plate, so it aligns with the frame. Turn on the water supply and position the mounting bracket with the plastic springs facing downwards, then secure using screws. 

Fit the mechanism into the bracket and connect the water supply line. Insert the flush plate starting from the bottom of the panel and make sure it’s securely in place. 

A full guide to fitting a mounted toilet can be found here.


Costs Of Toilet Plumbing  

  • Installing Or Replacing A Toilet 
    Installing or replacing a toilet can be challenging, depending on the exact model you have. If you choose to hire a professional, it will cost you anywhere between $400 and $800, depending on your model and location. If you decide to do it yourself, then it should only cost $150-$400 for the materials, but you will need to factor in the time taken.  
  • Toilet Repairs 
    Fixing a toilet will typically cost anywhere between $150-350, depending on the exact nature of the repairs. This includes the cost of labor for the repairs too. If you decide to undertake the repairs yourself, it may only cost as little as $100. Repairs come in all different shapes and sizes, but if you’re confident you can handle it, you could save yourself some money.  
  • Unclogging The Toilet 
    Unclogging a toilet can cost anywhere between $300 and $700 if you hire a professional. This will pay for the use of their specialized gear too. There are many different ways to unclog a toilet, and you may decide to save some money and do it yourself. Hiring some specialist kit will typically cost $100-150, and you may be able to do it with what you have at home.  

People Also Ask (FAQs)

Do toilets and showers use the same drain? 

They can use the same drain, but they don’t always, so this will depend on your configuration. Shower drains are typically only 2 inches, while toilets have 3 inch drains, so you will need to do some plumbing work to combine them.  

What happens if you don't vent a toilet? 

If you fail to properly vent a toilet, then the water pressure could be impacted. This will mean your wastewater is unable to drain from your home.  

Do you need silicone around a toilet? 

silicone or caulk coating around the toilet can help hold it in position and stop any water damage around the unit. This will help protect your toilet and keep it functioning for longer.  

What dissolves toilet ring wax? 

Specialist products can be used to dissolve toilet ring wax. A magic eraser is a common choice, but scrubbing with mineral spirits will also work.  

Can you plumb a toilet with PEX? 

Yes, PEX can be used to plumb a toilet and is generally a more affordable choice of pipe which is well suited for DIYers.  


Conclusion

Plumbing a toilet isn’t as difficult as it sounds, and you don’t have to rely on an expensive professional to do it for you. There’s quite a bit to think about it, but if you take it step by step, then it's manageable. Hopefully, this guide has given you everything you need to get started, and you're now able to successfully plumb your toilet. 

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.

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