Placing a PET bottle filled with water or sand inside the toilet tank is an old plumber's trick that reduces the volume of each flush and can save up to 300 liters of water per month, without any construction work, without replacing parts, and at zero cost.

Placing a PET bottle filled with water or sand inside the toilet tank is an old plumber’s trick that reduces the volume of each flush and can save up to 300 liters of water per month, without any construction work, without replacing parts, and at zero cost.

Written by Bruno Teles

Published on 28/05/2026 at 12:47

Updated on 28/05/2026 at 12:48

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The logic is simple: the bottle occupies a space that would be filled by water, so the tank fills with less liquid and uses less with each flush, without losing pressure. But there is a caveat that few mention: if the flush becomes weak and you pull twice, the savings simply disappear.

Placing a PET bottle filled with water or sand inside the toilet tank is an old plumber’s trick that reduces the volume of each flush and can help save water at home, without construction, without replacing parts, and with practically zero cost. A two-liter bottle represents about two liters less per flush, which, depending on household usage, can mean 300 to 480 liters saved per month with a single reused bottle.

The tip is simple and widely publicized by outlets like eCycle, Catraca Livre, and the Colabora project, and it works because the physics behind it is straightforward: the bottle occupies a space inside the tank that would be filled by water. Even so, as we will see, there is an important caveat that many sites forget to mention, which makes all the difference for the trick to truly work.

How the PET bottle trick works

The toilet tank, that reservoir attached to the wall just above the toilet, works by volume. When you flush, it empties completely and refills to the maximum level. If a bottle filled with water or sand is occupying part of this internal space, the tank reaches the full level with less water, reducing consumption with each flush without affecting the discharge pressure.

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Step-by-step to do it right

Before placing the bottle, it is essential to observe the interior of the tank, because there are parts that cannot be blocked, such as the float, the inlet valve, and the outlet mechanism. Choose a PET bottle of 1 to 2 liters, clean, well-capped, and completely filled with water or sand, so that it does not float or move with the water movement.

Next, open the lid of the box, identify where the mechanisms are, and position the bottle in a free corner, away from the float and valve, ensuring that it does not interfere with the movement of any part. Finally, flush a few times to confirm that everything continues to function normally. If you notice any jamming or strange noise, reposition or remove the bottle.

The caveat that few mention

Here is the point that many sites omit and that is fundamental for an honest assessment. Manufacturers and experts warn that this makeshift solution can fail and even make you use more water if the volume reduction compromises the cleaning of the bowl and forces you to flush twice in a row. In this case, the savings disappear, and consumption may even increase compared to normal.

Therefore, the trick requires common sense and testing. If, after installing the bottle, you notice that you need to flush more than once frequently, it’s a sign that you reduced the volume too much, and it’s best to use a smaller bottle or abandon the method. The idea is only worthwhile if the flush remains efficient with a single activation.

In which toilets the method works

Another important detail concerns the type of toilet. The trick works well in older coupled tanks, which usually have a capacity between 10 and 12 liters and, therefore, offer plenty of space for the bottle. In these models, there is excess volume, and the reduction does not compromise efficiency.

However, newer toilets, designed to consume only about 6 liters per flush, often do not accommodate the bottle because the internal space has already been optimized by the manufacturer. Trying to force a bottle into these models can disrupt the mechanism and cause malfunction. In other words, before applying the tip, it’s worth checking the capacity of your coupled tank.

The definitive solution is another

It’s important to make clear that the PET bottle is an immediate and zero-cost solution, but it’s not the most efficient in the long run. For those who are renovating or can invest a little, the dual flush mechanism, known as dual flush, is the most effective option, with savings that can reach 50% by allowing different volumes for liquid and solid waste.

According to industry manufacturers, such as Astra, dual flush systems offer a partial flush, around 3 liters for liquids, and a full flush, about 6 liters for solids, generating significant average savings and a noticeable reduction in the water bill. In other words, the bottle is a temporary fix, but investing in a good mechanism is what truly solves the issue in the long term.

Other Wastes That Go Unnoticed

The toilet flush often gets the blame, but it’s not the only source of waste in the bathroom. A discreet leak in the flush valve can waste hundreds or even more than a thousand liters of water per day without anyone noticing, silently inflating the bill.

A simple way to identify this problem is the dye or coffee grounds test: with the tank full and without using the toilet, put a little dye or coffee grounds in the tank water and wait. If the color appears in the toilet without anyone flushing, there is a seal leak that needs to be fixed. It’s a homemade test that helps catch the waste even before calling a plumber.

The PET bottle in the flush tank is one of those tricks that combine household savings and environmental awareness, tackling waste exactly where it happens, without relying on expensive technology or renovation. It works, it’s free, and can be done in a few minutes, as long as you respect the mechanism’s limits and the type of toilet. But, like any homemade solution, it has its limitations, and those seeking greater and safer savings should consider, in the future, a modern and efficient flush system.

And you, have you ever heard of or used the PET bottle trick in the flush tank? Do you have any other homemade tips to save water at home? Leave your comment, share your experience, and share the article with those who want to reduce their water bill without complication.

Placing a PET bottle filled with water or sand inside the toilet tank is an old plumber’s trick that reduces the volume of each flush and can save up to 300 liters of water per month, without any construction work, without replacing parts, and at zero cost.

The logic is simple: the bottle occupies a space that would be filled by water, so the tank fills with less liquid and uses less with each flush, without losing pressure. But there is a caveat that few mention: if the flush becomes weak and you pull twice, the savings simply disappear.

How the PET bottle trick works

Step-by-step to do it right

The caveat that few mention

In which toilets the method works

The definitive solution is another

Other Wastes That Go Unnoticed

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Placing a PET bottle filled with water or sand inside the toilet tank is an old plumber’s trick that reduces the volume of each flush and can save up to 300 liters of water per month, without any construction work, without replacing parts, and at zero cost.

The logic is simple: the bottle occupies a space that would be filled by water, so the tank fills with less liquid and uses less with each flush, without losing pressure. But there is a caveat that few mention: if the flush becomes weak and you pull twice, the savings simply disappear.

How the PET bottle trick works

Step-by-step to do it right

The caveat that few mention

In which toilets the method works

The definitive solution is another

Other Wastes That Go Unnoticed

With billions in loans, China is rebuilding Nigeria’s railway network from scratch, abandoning the British colonial tracks that have turned to scrap and creating a corridor of over 1,300 km to take the load off the roads of Africa’s largest economy.

A British company has installed in the middle of the ocean the world’s first floating platform that generates electricity 24 hours a day from the temperature difference between the surface and the depths of the Atlantic, without relying on wind or sun.

China is building an artificial island in the middle of the sea, covering 20 km², to construct the largest offshore airport in the world, the Dalian Jinzhouwan. This $4.3 billion project is anchored on more than 3,000 pillars embedded in the rock beneath the ocean and is scheduled to open in 2035.

Forget petroleum-based asphalt: a Scottish company transforms 684,000 plastic bottles into one kilometer of road that is 60% more resistant and up to 10 times more durable, and the technology has already started replacing traditional asphalt in more than 30 countries.

A robot named Walter does the work of five bricklayers per hour and can save the construction industry, where the average age of professionals is 46 years and almost no one wants to learn the trade anymore, in the United Kingdom.

Austrian engineers have developed an inflatable concrete technology that transforms flat slabs into domes using only air pressure, eliminating scaffolding and temporary forms, and potentially changing the way bridges, tunnels, and curved roofs are constructed worldwide.

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