What to Know Before Buying a Rear Outlet Toilet

Last Updated on July 14, 2023 by toilethaven

What is a Rear Outlet Toilet?

A rear outlet toilet, also known as a rear discharge or back outlet toilet, discharges its waste through the wall behind it, unlike a standard toilet, which drains through the floor. They are more common in high-rise apartments where doing plumbing work through the floor is more challenging and expensive.

 Apart from high-rise developments, rear outlet toilets are also increasingly being installed in private homes where the owner needs to remodel a bathroom or install a new toilet without digging up the floor.

These toilets can also be installed as an afterthought in places where you initially didn’t intend to have a toilet during the house construction. It is easier and cheaper to get the waste out through a wall than digging up and laying plumbing work in the floor.

How Do Rear Outlet Toilets Work?

In a rear outlet toilet, the waste outlet is connected to the wall hub fitting using a P-trap connector. When you flush the toilet, the waste flows through the wall and down to the city sewer line or septic tank.

They mostly use pressure-assisted flushing, which is powerful but a little loud than a gravity flush system. Unlike floor outlet toilets, rear toilets cannot create a strong siphon and hence the need to use a pressure-assisted flushing system.

A pressure-assisted toilet has a secondary tank inside the toilet tank called a pressure vessel which holds compressed air. Water flowing into the toilet tank mixes with the compressed air. When you flush the toilet, water under high pressure enters the toilet bowl flushing the toilet.  This is why the rear outlet toilets are loud during flushing.

Rear Outlets Toilets Vs. Wall Mounted Toilets

Wall-mounted toilets are toilets that are mounted on the bathroom wall where only the bowl is visible. The toilet tank is concealed in the bathroom wall and supported by a frame called a carrier, where the toilet bowl is also anchored. A thick wall is installed to conceal the tank and all the plumbing work.

A rear outlet toilet is floor-mounted, and its toilet tank is clearly visible. They are either one-piece or two-piece toilets.

Rear Outlet Toilets Vs. Floor Outlet Toilets

Floor outlet toilets are mounted on the floor on top of the drainpipe. A toilet flange is then installed on top of the drainpipe, which is used to firmly hold the toilet on the floor using bolts. A wax ring or rubber seal is placed between the bottom of the toilet and the flange.

A rear outlet toilet is mounted to the floor using two bolts on holes drilled through the bathroom floor. It does not have a flange or wax ring. Some rear outlet toilets are, however, installed using the same hardware as a standard floor outlet toilet.

What is the Best Rear Outlet Toilet?

It is not as easy to get a decent rear outlet toilet as it is to get a floor outlet toilet. There are so many floor outlets toilets to choose from.

I have been digging, and the following are some of the best rear outlet toilets available in the market today:

1. American Standard Yorkville




  • Elongated toilet bowl.
  • Two-piece toilet
  • Bowl height: 15 inches.
  • Toilet dimensions: 29.75D x 20.5W x 29.25H inches.
  • 4-inch rough-in.
  • 1.6 gallons per flush.

2. Kohler Barrington



  • Elongated bowl.
  • Two-piece toilet.
  • 4-inch rough-in.
  • Pressure lite flushing system.
  • EPA WaterSense.
  • Toilet dimensions:29.25D X 21.25W X 31.5H inches.

3. Signature Hardware Ebler




  • Elongated toilet bowl
  • Two-piece toilet
  • 15.5 inches bowl height
  • 1.6/0.8 gallons per flush
  • Rough-in: 6.5 inches
  • Toilet dimensions: 26.5D X 15.75W X 30.75H inches
  • Toilet seat included

4. Saniflo SaniAccess 3


Saniflo toilets are both rear outlet toilets and also upflush/macerating toilets. They can be installed in a basement (or just anywhere below the sewer line) or far from the sewer line.

Saniflo SaniAccess 3 is one of the best upflush toilet. Some of its features are:

  • Elongated/round toilet option.
  • Two-piece toilet.
  • 15 feet vertical pumping.
  • 150 feet horizontal pumping.
  • 1.28 gallons per flush.
  • Toilet dimensions: 28.5D X 17.25W X 31H inches.

If you would like to compare Saniflo SaniAccess 3 against other upflush toilets, please check out this post.

Rear Outlet Toilets Rough-in

It’s very important to make sure that you check out the rough-in of the rear toilet you want to buy. Different toilets have different rough-in measurements.

This is especially vital if you already have a rear outlet toilet in your bathroom that you want to replace with a new one. You want to make sure that the new toilet will fit where the old one was.

The rough-in of a rear outlet toilet is the distance from the finished floor to the center of the outlet pipe. You must make sure that you measure from the finished floor to have an accurate measurement.

The difference between the rough-in of rear outlet toilets and floor outlet toilets is that the rough-in of floor outlet toilets is measured from the rear toilet wall to the center of the drainpipe.

If you are going to buy an upflush toilet to double up as a rear outlet toilet, please note that their rough-in is different from a standard rear outlet toilet.

How Do You Install a Rear Outlet Toilet?

Rear outlet toilets are either one-piece or two-piece. With a one-piece toilet, the installation is easier, but with a two-piece toilet, it is a little harder. You will first need to install the toilet bowl and then install the toilet tank.

Materials Needed

  • Drilling machine with  the right bit
  • Screwdriver
  • PVC glue
  • Deep socket wrench
  • Adjustable wrench
  • Pencil
  • Rear outlet toilet P-trap connector

Step 1: Prepare the Toilet Tank

  • Slide a steel washer followed by a rubber washer on each of the toilet tank bolts. It is important you ensure that the washer that comes into contact with the toilet body is rubber. This prevents the toilet from cracking if you over-tighten it.
  • Feed the bolts through the inside of the tank into the mounting holes.
  • On the protruding ends of the bolts on the bottom of the tank, put in a rubber washer, followed by a metal washer, and finally, the nut.
  • Use the deep socket wrench to hold the bolts from inside the tank and tighten from under it using an adjustable wrench.

Step 2: Position the Toilet

  • Place the toilet bowl in the position where it will eventually be installed.
  • Using a measuring tape, measure the distance between the end of the toilet outlet and the wall hub fitting. This will help you determine the size of the P-trap connector. The connector should slide 1.5 inches into the wall hub fitting.
  • Once you have determined the length of the connector required, cut it into size with a hacksaw.
  • Using a pencil, trace the area occupied by the toilet bowl by drawing against its base.
  • Use the pencil to also mark two dots on the toilet bolt mounting holes.
  • Remove the toilet and place it away.

Note: Some toilets are designed to be installed by screwing in the bowl on the floor and also the toilet tank to the wall. In this case, the toilet tank will have two holes at the back. Use the pencil to mark the 2 dots against the wall (mount the toilet on top of the bowl)

Step 3: Drill the Holes

Use a drilling machine with the right size of bit to drill the holes to mount the toilet on the floor. If you will need to also secure the tank to the wall go ahead and drill the holes too.

Step 4: Install the Toilet

  • Apply PVC glue on the P-trap connector and slide it into the wall hub fitting.
  • Lift off the toilet and gently align and slide the waste outlet into the connector. Some toilets are quite heavy, and if you can’t manage to lift them on your own, please look for an extra pair of hands.
  • Insert the bolt and the washers into the toilet base mounting holes and tighten them with a screwdriver.
  • Cover the exposed part of the toilet bolts with matching bolt caps.
  • put the toilet tank gasket and install it on top of the tank. The 2 bolts should go in through the 2 mounting holes on the bowl.
  • put a rubber washer, steel washer, and a nut in that order and tighten with a wrench from underneath the toilet bowl.
  • If you have drilled holes in the toilet tank, put in the washers and bolts and tighten them.
  • Connect the water supply line to the toilet tank.
  • Turn on the shut-off valve (counterclockwise) and let the tank fill with water.
  • Flush the toilet a couple of times to ensure that there are no leaks.
  • Place the toilet lid on top of the tank.
  • Attach the toilet seat.

Step 5: Caulk the Toilet

Caulking or not caulking around the base of the toilet comes down to personal preference. The advantage of caulking is that it is easier to clean the joint between the toilet and the floor and also prevents water from flowing and collecting underneath the toilet. Caulking is also done for aesthetics.

Pros and Cons of Rear Outlet Toilets


1. Ideal for high-rise developments

The reason rear outlets are so ideal for apartments is due to the fact that you will not need a lot of floor space to accommodate the plumbing works. It, therefore, means more units can be constructed, which is more profitable than using floor outlet toilets.

2. Powerful flush

Although power-assisted flushing is not limited to rear outlet toilets, the siphon flush system is the most widely used flushing method in floor outlet toilets while the rear outlet almost always uses pressure–assisted flushing.

With these toilets, you will, therefore, not need to worry about your toilet clogging unless you flush something that does not need to be flushed.

3. You don’t need to remodel the bathroom floor

Demolishing a bathroom floor, doing the plumbing work, and rebuilding the floor is more expensive than just making a hole through the wall to install a rear outlet toilet.

4. They are versatile

You can install a rear outlet just about anywhere. A good combination is where you have an upflush and rear outlet toilet in one. A good example of this is the Saniflo Sanicompact toilet.

It is a compact, macerating, and rear outlet toilet that can pump waste up to 9 feet in vertical height. They are, therefore, an excellent toilet for a basement.


1. They are loud

The one thing you will notice about rear outlets is that they are louder while flushing than standard toilets. This is because of the force with which the pressurized water enters the toilet bowl.

2. The Toilet connector is visible

Unlike other sleek and skirted toilets where you do not see any plumbing work, the P-trap connector at the back of the toilet is clearly visible from the inside of the bathroom. This can be a turn-off for some people.