Frequently Asked Toilet Questions

How Does a Toilet Single Flush Valve Work? Best Explanation.

When the cistern is full, the flush valve seal sits across the bottom opening which would otherwise empty the water down to the toilet below. The cistern seal is held in place by the pressure of the water above. Meanwhile, the float on top of the seal is trying to lift the seal and let the water escape. The downward water pressure is greater than the lifting force of the float, so the seal stays in place and the water remains in the cistern.

How does a toilet flush valve work

When the handle/lever is pushed down, the attached chain lifts the seal, which allows the water to flow past the seal and down into the toilet bowl. Since there is now water below and above the seal there is no pressure from the water to push down on the seal and close off the water flow. The float is now free to lift the seal and keep the drain open while the water flows down into the toilet bowl. This happens even though the handle/lever may no longer be held down.

How does a toilet flush valve work

Once the water has emptied into the toilet bowl below there is no water left to lift the float. Gravity takes over and the seal once more falls shut across the opening.

The inlet valve now begins filling the cistern. The incoming water pressure holds the seal shut over the opening. As the water rises the float will try to lift the seal up. However, the water pressure bearing down is strong enough to overcome the float’s lift, so the seal remains closed.

How does a toilet flush valve work

The inlet valve will continue to fill the cistern until the incoming water reaches the correct level and shuts off. The cistern is “loaded” with water until the next flush.

How Does a Toilet Dual Flush Valve Work? Best Explanation.

A dual flush valve is slightly more complex than the single flush unit but works on the same principle. Instead of one float there are two.

Modern dual flush valves are usually cylindrical in shape. The full-flush float is positioned at the bottom of the cylinder, as with a single flush valve, and is connected to the full flush button positioned above on the cistern lid. The second float is positioned half way up the valve body and is connected to the half flush button above. Both the full-flush float and the half-flush float are connected to the seal below. They are not however connected to each other and lift the seal independently of each other. Refer to the diagram for the details.

How does a dual flush toilet valve work

When the full-flush button is pushed down, it raises the float at the bottom of the cistern. This float is connected to the seal which lifts and remains open until the water has drained down to the toilet below. Once the cistern empties, the float drops. This causes the seal to drop shut and the incoming water again fills the cistern (as with the single flush valve described above).

When the half-flush button is pushed down, the half-flush float is raised. This float is also connected to the seal which is raised and remains open until the water drains below the level of this float. Once the half-flush float is exposed by the falling water, it drops, returning the seal to its closed position. The inlet valve then fills the cistern to the required level.

Whilst each float is connected to the seal, they work independently of each other.

How do I Adjust the Amount of Water Which is Used by my Toilet in the Half Flush Mode?

Because the half-flush float is the one which sets the half-flush level, the height of this float controls the volume of water released in a half-flush operation. The higher the half-flush float is positioned, the less water will be released through the seal into the toilet below. The lower the half-flush float is positioned, the greater volume of water will be released per half-flush cycle. 

Dual-flush valves usually allow for adjustment of the height of the half-flush float. Check the manufacturer’s guide to determine how to adjust the half-flush float level. Some of them require a twist before they can be adjusted, others have a button on the side which releases the half-flush valve for positioning.

My toilet is leaking, what can I do about it?

When a toilet leaks, it will usually leak into the bowl and the water will drain away. This is better than flooding the house however it can still be very expensive as leaks run 24/7. The cost can run into thousands of dollars. There are two main causes of leaks. The first cause is the inlet valve and the second is the flush valve.

How can I find what is causing my toilet to leak?

There are two main causes of cistern leaks into your toilet bowl. The first cause is the inlet valve and the second is the flush valve.

If a faulty inlet valve is causing the problem, then water will pass constantly into the cistern from the supply hose (usually a braided stainless steel flexible hose). The level of the cistern water will rise until the excess flows into the overflow tube. This tube is connected to the flush valve and bypasses the seal to flow down into your toilet bowl. To diagnose this fault, look into the cistern to see if the level is so high that excess water is running into the overflow pipe.

If the flush valve is the problem, the water in the cistern will leak through the valve seal and run down into the bowl. The outflow of water through the leaky seal will lower the cistern level until it causes the inlet valve to open and allow in more water to make up the volume. This cycle of inflow and overflow will continue until the leaky valve is replaced. The common way to diagnose this problem is when the house is quiet, to listen for the stop-start sound of the inlet valve re-filling an apparently full cistern.

How can I stop my toilet from leaking?

The solution depends on whether it is the flush valve causing the problem, or the inlet valve.

How can I fix a leaking flush valve?

When a flush valve is leaking there are two choices. You could try to replace the flush seal, or you can replace the whole valve.

Is it a good idea to just replace the flush seal?

Replacing the flush valve flush seal seems a cheaper option. However, in our experience, by the time the flush valve is leaking it is best to consider a replacement valve rather than fiddling about with the expense and time of replacing a small seal. Often, the valve’s other plastic parts have become brittle or distorted with age so the whole unit is defective.

Flush valves are not costly. Once the job is done the new valve will give many years of service. If you are using a plumber for the work (as you should in Australia), then the labour costs will far outweigh the cost of the valve.

What are my options if I have to replace the flush valve?

If you can find the same type of flush valve, then replacement should be a simple operation. Most valves will unclip near the bottom and the new top part of the valve can be simply clipped on to the existing basket. Click on "Flush Valves" on the blue ribbon above to identify your valve.

(If you are unsure as to the make of your flush valve, just take a few photos with your phone and send them to us at or text to 0415 614 847 for identification and matching from our stock.)

If you cannot find an exact replacement for your flush valve, you may be able to replace the entire valve with a similar model, providing your toilet system is the two piece, “close coupled suite.”

A “close-coupled suite” means that the cistern unit sits directly on top of the toilet bowl and can be removed by unscrewing the two wingnuts under the cistern.

See a video of how to do this HERE

How can I Fix a Toilet Inlet Fill Valve?

Some toilet inlet valves can be fixed by replacing just the diaphragm. However due to the time involved and the relative cost of parts compared to the modest cost of a new valve, we strongly advise replacement of the whole inlet valve.

Fill/inlet valve replacement is a fairly simple operation. First turn off the water supply to the cistern. Once this is done, the inlet hose (usually a braided stainless-steel hose) can be removed from the valve and the valve unit replaced.

Details vary slightly between models so check manufacturers recommendations. If not sure, give us a call on 0415 614 847