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Rough Plumbing for Rear Discharge Toilet (Ultimate Guide)

Rough plumbing for a rear discharge toilet is a bit more complicated than for a standard toilet, but it is still a relatively straightforward process. 

Rough plumbing is essentially the same as for any other toilet, with a few minor differences. The main difference is that the waste pipe for a rear discharge toilet drain sits in a different location.

Rough Plumbing for Rear Discharge Toilet

What Is a Rear Discharge Toilet?

A back drain toilet is a type of toilet that discharges waste through a pipe at the rear of the toilet rather than through a hole in the floor. Rear discharge toilets get used in commercial applications. They can also work in residential homes.

If your home sits a reasonable distance away from the sewer lines, rear discharge toilets are a great option. They provide an easy way to connect the waste from the toilet to those lines.

Not to mention, they cost less to install than standard toilets.

How Long Does the Replacement Process Take?

Rough plumbing for a rear discharge toilet can take a few hours. The process, from start to finish, should take no longer than a day. Cut down on time by ensuring you have all the necessary tools and materials before you begin.

Considerations for Rough Plumbing for Rear Discharge Toilet

There are several things that you need to take into consideration if you decide to do rough plumbing for your toilet.

Proper Waste Pipe Size

The first is that the waste pipe needs to be large enough to accommodate the waste from the toilet. It means that you will need to use a larger diameter pipe than you would for a standard toilet.


The second is that the waste pipe needs proper ventilation so that sewer gasses do not build up in the home. Accomplish this by venting the pipe to the outside of the house. Or, run a vent stack up through the roof.

Location of the Toilet

The third consideration is the location of the toilet. Rear discharge toilets must sit near a waste stack or a sewer line. This is so the waste pipe can adequately connect to the sewer system.

Location of the Toilet

Proper Pitching

In addition, the waste pipe requires proper pitching so that waste will flow smoothly through it. Accomplish it by using a drainpipe slightly larger in diameter than the waste pipe or by installing a cleanout fitting in the waste pipe.

Rough Plumbing Dimensions

You also need to make sure that the drain pipe is installed at least 12 inches above the floor. The waste pipe installation must sit at least 18 inches above the floor. 

These measurements come directly from the National Plumbing Code.

Steps for Rough Plumbing for Rear Discharge Toilet

Now that you know the considerations for rough plumbing for a rear discharge toilet, here are the steps you need to take to do it correctly.

Let’s start with the tools and materials you will need to do so.

Tools and Materials Needed

  • A pipe wrench, an adjustable wrench, and a hack saw
  • Channel locks, tape measure, and a level
  • Shims, dielectric unions, and a drill with a 1/2″ drill bit
  • Pipe cutter, copper pipe, a wire brush, and brass fittings

Finally, you will also need to have a soldering torch, solder, and flux to aid in your rough plumbing journey. Soldering is a great skill to have and there are many variations.

Step 1

The first and most significant step is shutting off the toilet’s water supply. It can be done by shutting off the water at the main shutoff valve for the home or by shutting off the water at the shutoff valve for the toilet.

Step 2

After turning off the water supply, flush the toilet to empty the tank and bowl. Next, disconnect the water supply line from the toilet by loosening the nut that secures it with a pipe wrench.

Step 3

After the water supply line is disconnected, remove the tank from the bowl by loosening the nuts that secure it. The bolts sit under the tank and usually stay in place with nuts. Be cautious not to cause damage to the bowl when removing the tank.

Step 4

You will need to remove the old waste pipe. To do this, first, remove the cleanout plug from the waste pipe. It will give you access to the cleanout fitting.

Use a pipe wrench to slacken the nut that secures the cleanout fitting to the waste pipe. Once the nut starts to loosen, you can remove the cleanout fitting and the waste pipe.

Step 5

Start installing the new one. Begin by measuring the distance from the center of the drain to the waste stack or sewer line. It will be the length of your new waste pipe.

Cut the copper pipe to the correct length using a pipe cutter. 

Next, clean the ends of the pipe with a wire brush to remove any burrs. Burrs can cause soldering problems later on. 

For example, a slight burr on the end of the pipe can create a hole in the solder joint.

Tools and Materials Needed

Step 6

Once the pipe gets cut to the correct length and the ends are clean, you can begin installing the new waste pipe. To do this, start by attaching a dielectric union to one end of the pipe.

A dielectric union is a fitting used to connect two different types of metal. It is essential because it will prevent dissimilar metals from coming into contact with each other and causing corrosion.

After the dielectric union is in place, you can attach a 90-degree elbow to the other end of the pipe. The elbow should be pointing toward the waste stack or sewer line.

Step 7

Now, you can attach the other end of the pipe to the waste stack or sewer line. To do this, you will need to use coupling. A coupling is a fitting used to connect two pieces of pipe.

Step 8

Once the coupling is in place, attach a dielectric union to it. It will complete the connection between the new waste pipe and the sewer system.

Step 9

Now that the new waste pipe installation has finished, you can reattach the tank to the bowl. Start by threading the bolts through the holes in the bottom of the tank.

Once the bolts are in place, you can attach the nuts and tighten them with a wrench. Be sure to tighten the nuts evenly so that the tank is level.

Step 10: Final Step

After the tank is attached, you can reattach the water supply line. To do this, simply thread the nut onto the supply line and tighten it with a wrench.

Once the water supply line is attached, you can turn the water back on and test the toilet. 

If everything moves as it should, you can now enjoy your newly installed rear discharge toilet in peace.

Wrapping Up

Installing a rear discharge toilet is not difficult, but it is essential to do it correctly. 

Follow these steps to ensure correct toilet installation and functions. The installation of a rear discharge toilet is a job that most homeowners can do on their own, but it is always best to consult a professional if you have any questions or concerns.

If you found this article helpful in installing a rear discharge toilet, please share it with your friends and family. Leave any questions or experiences regarding this process in the provided comment section below.

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