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What is a Pressure-Assisted Toilet?

L. S. Wynn
By L. S. Wynn
Updated May 16, 2024
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The mechanisms within conventional toilets have not changed much since they were invented, but recently, a new generation of toilets has become available. Pressure-assisted toilets use compressed air to move waste products, rather than relying on gravity to do the work. This means that the bowl is typically cleaned more quickly and thoroughly, using less water.

Traditional, or gravity, toilets work in a very straightforward manner. Water is stored in a tank above the bowl and when the flush lever is pressed, the water is released under the force of gravity into the bowl and the waste is removed. From the outside, pressure-assisted toilets look identical to gravity toilets, but when someone lifts the lid, however, instead of seeing water, he will notice an inner tank.

The tank is completely sealed; when water is fed from the water line, the air inside the tank gets compressed. When the toilet is flushed, instead of just falling by the force of gravity, the water is forced out with the pressure of the compressed air. This pressurized stream of water cleans all the waste from the bowl much more efficiently than the water from gravity toilets. The pressure in the toilet is created by using the water pressure provided by the water company — no pumps or other devices are used.

Pressure-assisted toilets are more expensive than gravity toilets, but they do a better job of removing waste from the bowl with less water. The first generation were very noisy and some were not very reliable, but most of these hurdles have been overcome.

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Discussion Comments
By anon990203 — On Apr 10, 2015

I have a Kohler pressure assist toilet that seems to have too much pressure and water is shooting out of the bowl. Is there a way to adjust the pressure to a lower setting?

By anon972127 — On Oct 01, 2014

As previously stated, many manufacturers carry models in colors other than white -- linen and bone being the other two choices readily available.

You cannot retro fit a gravity fed toilet with a pressure assist. The bowl is specially designed with a larger trap way that allows the water to be pushed and only has one bend. Gravity fed toilets create a siphon and have several bends to achieve the suction necessary for evacuation.

Conversely, because of the difference in design, I don't believe you can have a proper functioning pressure designed toiled with a gravity fed water tank supplying the pressure. It cannot develop enough force to push the waste out. Again gravity fed toilets are designed to evacuate using a siphon action and must be designed as such.

Pressure requirements are modest. The 1.6 L models need only 20 psi of pressure while the 1.28 or 1 L models require 25 psi.

The requirements for installation are the same as for normal gravity feed toilets. Manufacturers have spec sheets you can consult.

For the person with water shooting up: it may be coming from a loose air inductor cap. Try tightening it by hand. Flush and observe to see if that fixes the problem. It is normal for some water to be in the bottom of the china tank but is emptied with a special drain when it reaches over 1 inch. If the water continues to shoot out, it the duck bill valve on the air inducer may be damaged, upper water hose cracked or lower water supply may be cracked and need replacing. You will need to observe and trouble shoot.

By anon352455 — On Oct 22, 2013

How can I increase the pressure in the pipe (shower) that is used for cleaning the skin.

By tacktack — On Dec 20, 2012

Can I remove the pressure tank and replace it with a regular kit?

By anon300801 — On Oct 31, 2012

Can a regular toilet be retrofitted with a pressure

assisted kit without a problem?

By anon294522 — On Oct 02, 2012

If a pressure assisted toilet gets clogged for some reason, is it normal for the water to then overflow from the bottom of the toilet and also through the ceiling into the downstairs bathroom beneath it?

By anon161042 — On Mar 18, 2011

I have a low pressure, well pump system, something less than 40 pounds of pressure in the line. Is it possible that a pressure assist toilet will work or do I need to purchase one that has an electrical assist pump?

By anon157866 — On Mar 04, 2011

I have a pressurized toilet. (First one.) I notice now that when I flush the toilet that water leaks from under the tank lid. Is there supposed to be a lot of action in the porcelain tank? Or could there be an obstruction causing this?

When I flush the toilet without the lid there is a lot of water that shoots up one side of the tank and then out the top. Help!

By anon156491 — On Feb 27, 2011

I have a sewer ejector because my toilet is below sewer lines. Do I also need a pressure-assist toilet or will a gravity toilet work just as well.

By cduggins — On Oct 19, 2010

should these toliets work as well in the country with a well distributing the water?

By anon74033 — On Mar 30, 2010

Pressure assist toilets have special bowls. You cannot retro-fit your gravity fed bowl with a pressure assist tank. The bowl will splash excessively.

As for the comment about drain line not being rated for pressure. That is correct for all drains, but as soon as the water enters the bowl the pressure is released. The only thing entering the drain is flow, gallons per minute. So you do not have to be concerned about the drain pipe pressure rating when installing a pressure assist toilet.

By anon43230 — On Aug 26, 2009

In an application where rapid flushes are the norm and water is available can the water bladder/tank be air pressurized to get an higher pressure flush? meaning could the air supply to a filled bladder/tank be adapted?

By anon37213 — On Jul 17, 2009

Crautiola - You need to install a sewage ejector to make your basement bathroom work. It's basically a large plastic tank that you would install under the basement floor. In the tank is a pump that delivers the waste up out of the tank and into your sewage line. This would involve breaking up a section of your basement floor and digging a 4 foot deep hole.

By dleasus71 — On Mar 19, 2009

Can a gravity fed toilet be retrofitted to be a pressure assisted toilet?

By Crautiola — On Feb 09, 2009

I am a diy-guy(although learning as I go...). I hope to install a toilet and sink in my basement. However, the sewer line discharge from my basement is 4' above the basement floor. The current PVC drain lines are "non-pressure" rated.

What are practical options for this challenging starting point?

By n182hw — On Jun 14, 2008

The standard type toilets must be replaced to use a pressure assisted toilet the casting of the bowl is different. No other plumbing requirements are needed. These things really work well, no need for additional flushes.

By dbarb — On Apr 20, 2008

In one of the bathrooms at our church there are 3 toilets, two conventional gravity flush, and one pressure assisted flush. The bowls of all three appear to be the same. The tanks on the conventional flush toilets seem to empty slowly, and sometimes "flush" more than once because the water in the tank is being replaced relatively quickly before the flapper seats. question: Is it possible that the bowl (Kohler approx 1995) is designed for a pressure flush and should not be set up for gravity flush?

By anon4132 — On Oct 04, 2007

Can a conventional toilet be retro-fitted with a pressure assist inner tank? If so, where could a retro fit tank be bought?

By anon3901 — On Sep 23, 2007

Are these toilets a drop-in replacement to traditional (gravity) toilet, or do I need special fixtures, plumbing mods. In other words, is there anything different I need to do when I replace a traditional (gravity) toilet?

By rjohnson — On Sep 19, 2007

Pressure-assisted toilets come in the same variety of colors as regular toilets. Kohler® and Gerber® are two brands, for example, that carry non-white pressure-assisted toilets.

By anon1020 — On May 11, 2007

Do pressure-assisted toilets come in colors (other than white)?

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