How to Build a Wheelie Bin Rainwater Tank with a Self-Flushing Overflow

A spare wheelie bin can be converted into a compact rainwater tank for watering the garden. A 220-litre bin holds approximately 220 litres (58 US gal) of water, making it useful where there is not enough space for a conventional rainwater tank or where a small additional storage tank is needed.

This was the first rainwater storage system I built, and the original design gradually became more elaborate as I experimented with ways to improve it. The final version included an inlet filter, a tap, an overflow and an unusual bottom-draw overflow designed to discharge water from near the base of the tank rather than simply allowing newly arrived rainwater to spill from the top.

That last feature is the most interesting part of the design. It allows an overflow event to replace some of the older water at the bottom of the tank and carry out loose sediment around the pickup point. This is a self-flushing bottom-draw overflow. It can help remove loose sediment, but it does not eliminate the need for occasional tank inspection and cleaning.

NOTE: To avoid unnecessary repetition, the construction steps in this project are slightly abbreviated, as I’ve already covered the construction methods, tools and techniques in great detail in the previous project, a modular, expandable water tank system – listed here Recycled Plastic Drum Rainwater Tank under “DIY Instructions“.

How the Wheelie Bin Rainwater Tank Works

A simple rainwater tank requires only three basic components: an inlet to bring rainwater into the tank, an outlet or tap to draw off the stored water, and an overflow to safely discharge excess water once the tank is full.

A roof downpipe or rainwater diverter directs rainwater into the top of the wheelie bin via a screened inlet. A tap near the bottom allows the stored water to be used to water the garden.

When the tank is full, excess water drains through an overflow fitting near the top.

A conventional overflow draws water from the surface of the tank. As fresh rainwater enters, the water level rises until the newest water spills through the overflow.

The bottom-draw overflow works differently.

Instead of leaving the inside of the overflow fitting open, a pipe runs from the overflow fitting down to near the bottom of the tank. When the water level rises above the overflow level, water near the bottom is forced up this pipe and out through the overflow.

This serves two purposes:

1. It provides the normal overflow required to prevent the tank from overflowing through the lid.
2. It replaces some of the water near the bottom of the tank and can carry loose sediment from around the intake out with the overflow water.

This is an example of the permaculture principle of designing one element to perform more than one function.

How the Bottom-Draw Overflow Works

The operating principle of a self-flushing bottom-draw overflow system is based on simple hydrostatics.

The diagram below shows how it works.

1. Rainwater entering the tank raises the water level, and it cannot escape until the level reaches the overflow outlet. If the overflow outlet were just a hole on the side of the tank, water would naturally flow out from the top once the water level slightly exceeds the hole’s bottom edge.
2. Adding a bottom pickup pipe—a vertical pipe running from near the base of the tank to the overflow fitting—allows water to be drawn from the bottom of the tank during overflow, while still maintaining an overflow outlet on the side of the tank.
3. When the water level rises inside the tank, it also rises the same level inside the pickup pipe.
4. As soon as the water level inside the tank reaches the level of the overflow pipe — the pipe that carries discharged water away from the tank — it also rises to the same level inside the vertical pickup pipe and flows out through the overflow pipe to the ground.
5. As rain flows into the tank, the water level rises above the overflow fitting. Water can then flow from near the bottom of the tank, up through the pickup pipe and out through the overflow. The higher water level in the tank provides the pressure that drives the flow.
6. The suction through the pickup pipe at the bottom of the tank works like an underwater vacuum cleaner, drawing out the dirt and sediment along with the water at the tank bottom.

An important complication arises when the bottom pickup pipe is connected directly to the overflow pipe. If the external overflow pipe extends below the tank and begins to fill with water, it will create a siphon. This siphon will continue drawing water even after the tank water level drops below the overflow. Once it starts, the water will keep flowing out, draining the container completely. I learned this through experience—after the tank drained itself once the water flow started through the overflow pipe.

An air vent or siphon break, usually a “T”-shaped irrigation fitting, is fitted at the high point of the internal overflow assembly. Once the water falls back to below the level of the overflow outlet, it allows air to enter the pipe to stops the siphon action and the water flow. It’s a simple but effective fix!

Design Theory

This project offers a quick guide to basic water tank design and explains how to build a simple self-cleaning system that automatically removes sediment from the tank bottom during overflow. The design can be adapted to any water tank, including large commercial storage systems.

Aligning with the permaculture principle of having things serve more than one purpose, this design uses the overflow outlet of a single tank to fulfil two roles:

1. To redirect excess water that cannot be stored to other storage locations or to the garden
2. To remove stagnant water and dirt from the bottom of the tank

Overflow outlets are usually located near the top of the tank. When the tank fills, excess clean rainwater flows out through a flexible pipe to another location, ideally for use elsewhere rather than draining into the stormwater system.

If all water storage options have been exhausted, the most obvious one used by nature—soil—should be considered. Soil can hold a significant amount of water. When tanks are full and rain is forecasted, pumping water into the soil instead of losing it is advisable. Letting rain naturally refill tanks optimizes stormwater usage. Unless in one of Australia’s wetter regions, there is little risk of turning the garden into a swamp.

The main issue with traditional overflows is that the fresh, oxygen-rich water that is collected is immediately expelled, while the older, stagnant, oxygen-deprived water remains at the bottom of the tank. This stagnant layer, full of sludge and sediment, provides an ideal environment for less-friendly bacteria to thrive.

If the incoming fresh water could be used to displace the old, stagnant water and remove some dirt and sludge, that would be ideal! And that’s precisely our goal here.

Construction

Building a wheelie bin water tank is quite simple and straightforward. You can create a basic water storage unit by completing just a few steps. The remaining steps are optional and can be done anytime to enhance functionality.

Materials Required

For the basic water tank:

• One clean, undamaged wheelie bin, preferably new or with a known uncontaminated history
• One removable inlet strainer or approximately 200 mm (8 in) aquatic water garden basket pot
• One 20mm threaded tank adapter or bulkhead fitting for the tap
• One garden tap or ball valve
• Appropriate hose adapter, if a garden hose will be connected
• Thread-sealing tape where required by the fittings

For the water tank overflow:

• One 20mm tank adapter or bulkhead fitting
• Overflow pipe of the appropriate diameter
• One 20mm 90-degree elbow for a conventional overflow

For the optional bottom-draw overflow:

• One 20mm tee fitting the same diameter as the overflow pipe
• One 20mm 90-degree elbow
• One length of 20mm rigid irrigation riser tube extending from the overflow fitting to near the bottom of the tank
• A short vent pipe or equivalent air-break arrangement

For the roof connection:

• Rainwater diverter, rainhead or suitable downpipe connection
• First-flush diverter where appropriate
• Suitable rainwater pipe connecting the roof drainage system to the tank

Tools Required

The work requires only basic tools:

• Electric or cordless drill
• Hole saw 25mm for the 20mm tank fittings
• Electric jigsaw, keyhole saw or another suitable tool for cutting the inlet opening
• Tape measure
• Marker
• Adjustable spanners
• Fine sandpaper or a deburring tool
• Saw suitable for cutting the overflow pipe

Step 1: Select the Wheelie Bin

First, obtain a wheelie bin, whether new or recycled, to contain the water.

Begin with a sound wheelie bin that has no cracks, splits, badly degraded plastic, or damaged seams. Since a full wheelie bin can be quite heavy (220kg for a 220-litre bin – water weighs 1kg per litre), it might burst if its structure is weakened.

This design can be effortlessly customized and adapted to suit any type of water container.

Step 2: Prepare the Inlet Filter – Water In!

A medium-sized, 20cm aquatic basket pot, commonly used in water gardens and ponds, functions as the water inlet filter.

This removes large debris, such as leaves, before it reaches the tank and prevents mosquitoes from entering and breeding in the water tank. The basket pot can be lined with shade cloth for even finer filtration.

Step 3: Cut the Inlet Opening

A hole needs to be cut into the lid of the bin to fit the water inlet filter (the aquatic basket pot).

1. Place the basket or inlet strainer on the wheelie-bin lid and mark the opening.
2. Cut the hole with an electric jigsaw or any other suitable hand saw that can cut curves, such as a keyhole saw.
3. Remove any rough edges.

Note: The opening should be sufficiently large to allow the body of the basket to pass through, yet smaller than its upper flange to ensure the basket rests securely on the lid instead of slipping into the tank. The pot features a wider lip, which helps support the pot’s position.

Step 4: Fit the Inlet Filter

Fit the water inlet filter (the aquatic basket pot) into the hole in the lid of the wheelie bin.

It should be a nice snug fit with no gaps around its edge.

Step 5: The Outlet – Water Out!

Now that we can get water into the bin, we will also need a way to get it out! To fit a tap to the tank, we will need a 20mm threaded tank adapter or bulkhead fitting, as pictured below. The tap screws into this fitting.

Step 6: Mark the Position of the Tap

Mark the drilling location for the outlet tap on the wheelie bin. The outlet should be positioned around 10 cm (4 in) above the bottom. For this project, the tap has been placed 10 cm (4 in) from the bottom edge of the front, and centered.

Positioning the tap just above the floor creates a small gap underneath, allowing sediment to settle instead of going directly into the tap.

The outlet can be installed on the front or side, depending on the tank’s location. The tap can be placed wherever needed. If space is limited and front clearance is necessary, it can be positioned on the side, for example.

Before drilling, ensure there’s sufficient space inside the bin for the tank adapter and adequate clearance outside for the tap or ball valve.

Step 7: Drill the Outlet Hole

To drill a precise, hole for the threaded adapter that will be watertight once it is fitted, use an electric or cordless drill equipped with a holesaw (as pictured below) or a step drill.

1. Select a hole saw that matches the required cut-out diameter for the particular tank adapter.
2. Drill the hole at the marked location.
3. If there are any rough edges or burrs around the edges of the hole after it has been drilled, carefully smooth them off both inside and outside the tank with fine sandpaper. A tank fitting seals against the surface of the container, so a rough or distorted edge can prevent the washer or gasket from sealing properly.

Do not make the hole larger than necessary.

The outer diameter of the 20mm threaded tank adapter is 25mm, so drilling a hole with a 25mm holesaw will provide a snug fit.

Step 8: Fit the Tank Adapter

1. Insert the 20mm threaded tank adapter through the tank wall, ensuring the sealing washers or gaskets are on both sides of the tank. Place the softer rubber washer inside the tank to create a seal in the water area, and position the tougher washer outside, as it is more durable and resistant to sunlight degradation.
2. Tighten the 20mm threaded tank adapter with two adjustable spanners, one on each side, that is, one inside the tank and one outside. Tighten the fitting sufficiently to compress the seal, but do not overtighten. Excessive force can distort the wall of a plastic container or damage the washer.

How to Use Teflon Tape on Threaded Plumbing Joins

Threaded irrigation fittings and taps, like the ones described in the next steps below, need to be sealed with Teflon plumber’s thread-sealing tape before they are screwed together. The tape fills the small gaps between the mating threads and helps prevent water leaking through the threaded joints.

Here are a few tips on how to use Teflon plumber’s thread sealing tape on threaded (screw) joints of irrigation fittings to create watertight joints that won’t leak:

1. Hold the threaded fitting in your left hand with the threaded end facing towards you, as shown in the picture.
2. Hold the roll of Teflon tape so it resembles a snail, with the tape feeding from the bottom of the roll. This makes it easy to keep the tape under tension as it is wound around the fitting.
3. Starting near the end of the threaded section, but without covering the opening, lay the tape across the threads.
4. Looking at the end of the fitting, wind the tape clockwise, following the direction of the threads. Keep the tape under light tension as you work along the threaded section, overlapping each turn slightly.
5. Apply around seven turns of tape, then tear it off and press the loose end firmly against the threads.

The direction in which the tape is wound is important. These fittings screw together clockwise, so wrapping the tape clockwise means that tightening the fitting also tightens the tape around the threads. If the tape is wound in the opposite direction, it can bunch up or unwind as the fitting is screwed into place.

Holding the roll “snail-wise”, with the tape feeding from the bottom, also makes the job much easier. The tape can be kept taut against the threads while winding. If the roll is held the opposite way, the tape tends to unroll ahead of the fitting and is much harder to keep tight and neatly wrapped.

Keep the tape entirely on the threaded section and do not wind it across the opening of the fitting, where loose pieces could be pushed into the pipework when the fittings are assembled.

Note: Connections sealed with a rubber washer or an O-ring, like the screw-on hose click fittings at the end of a tap, do not require Teflon tape, as the rubber washers or rings effectively seal the connection.

Step 9: Fit the Tap

To control water flow, a tap or ball valve is needed. The ball valve opens completely with a quarter turn of the lever, offering convenience, but it is more expensive than a standard garden tap, which works just as effectively.

When buying a brass garden tap, select one with the correct-sized threaded outlet (where the water comes out and a hose connects), as these come in two sizes, 19mm (3/4″) and 25mm (1″).

In all Australian states, the standard brass garden tap outlet size is 3/4″, except for NSW, where a 1″ outlet tap is used.

When purchasing the fittings, make sure the tap or ball valve screws into the 20mm threaded tank adapter. If it doesn’t, additional fittings will be needed, so make sure these are all on hand before commencing!

The threads at the back of the tap should screw directly into the hole at the end of the tank outlet. If the threaded section at the back of the tap is too small to fit the tank outlet, a reducing bush—a threaded plastic adapter—can be used to screw a smaller fitting into a larger hole.

To attach the tap to the 20mm threaded tank adapter:

1. Wrap the threads of the tap with teflon thread sealing tape (as shown below) for a watertight fit.
2. Screw the tap or ball valve into the to the 20mm threaded tank adapter (bulkhead fitting).

An additional hose fitting can be attached to the tap if required. Keep in mind that a gravity-fed water tank provides much lower water pressure than a mains-connected garden tap, so water will flow through a hose more slowly, particularly if the hose is long or runs uphill. It will also not flow higher than the water level in the tank!

This is the finished outlet tap setup. I’ve installed a few additional fittings so I can connect a garden hose directly to the click-fitting at the end.

At this point, the wheelie bin can already function as a very basic rainwater tank. It has an inlet and an outlet, it will collect and dispense water, and if that is sufficient, then the project is complete.

It still requires an overflow before connecting to a roof catchment. If you’d like to add some “few more bits,” continue reading…

Step 10 – Install the Overflow Fitting

An overflow is an additional outlet positioned higher on the tank’s side, allowing excess water to escape when the water level reaches it. This prevents water from spilling over the top of the tank and flooding the area around it once the tank is full. By attaching a pipe to the overflow outlet, the excess water can be directed to a drain, garden, lawn, another tank, or any preferred location.

To install the overflow fitting:

1. Mark the overflow position near the top of the bin, at the level where the water should drain out. The bottom of the overflow opening determines how high the normal maximum water level will be. Leave enough space above this level so incoming water does not immediately reach the underside of the lid.
2. Drill the overflow hole using the same method as for the tap fitting, with a drill fitted with a holesaw.
3. Fit another 20mm threaded tank adapter to the overflow tank fitting.
4. Screw a 20mm elbow fitting (“L”-shaped) to the 20mm threaded tank adapter. Use Teflon plumber’s tape on the threads, screw it together, and turn the elbow fitting so the external opening of the water outlet points down.
5. Attach the necessary fittings to the 20mm elbow for the type of hose being used. A washing machine drain hose is an inexpensive and effective option, and the rubber fitting can be slipped onto a 20mm fitting to secure it.

These overflow fitting pictures are from the more detailed Recycled Plastic Drum Rainwater Tank project:

Your tank is now set up with a reliable basic overflow, just like the one on my main water collection system, and it’s effectively “flood-proof”. If you’re happy to keep things simple, you can stop here—but if you’d like to add extra features for even better performance and ease of use, read on for the next practical steps.

Step 11: Build the Self-Flushing Bottom-Draw Overflow

The image below shows the siphon cleaning system installed inside the wheelie bin tank. The overflow draws water and sediment from the anaerobic zone at the tank’s bottom and directs it to the stormwater drain or another outlet.

NOTE: In the picture below, the overflow on the left is capped and turned upwards because the tank was temporarily disconnected from use. This is a preventative measure to prevent mosquitoes from entering and to avoid long-term water stagnation in the fitting. Normally, it points downwards with an overflow pipe connected, as shown in the other photos below.

To set up the overflow siphon:

1. Attach a 20mm “T-piece” to the overflow 20mm threaded tank adapter inside the tank. This serves as an air vent or suction breaker, allowing air to enter the overflow pipe and preventing the tank from self-draining when water flows through it. Point the top of the 20mm “T-piece” upwards.
2. Next, attach a 90-degree or elbow joint (“L”-shaped) to the opposite side of the 20mm “T-piece”, then angle the elbow joint downward so that the open end points toward the bottom of the tank. The vertical pickup pipe will be attached to this.
3. Sit a 20mm irrigation riser tube inside the tank, beside the elbow joint, running vertically downward until its lower end is close to the floor of the tank. This will be the the pickup pipe, which will need to be cut to length before fitting. For a 220-litre bin, it should be approximately 60cm long and when connected to the elbow joint should reaches the tank’s bottom. Trim the tube if needed for a proper fit. It can sit at an angle, as long as it contacts the bottom.
4. Once the pickup pipe is cut to length, cut several notches into the lower end of the pipe so water can enter even if the pipe rests against the tank floor, as shown in the diagram below. This assists water flow and sediment collection while preventing blockage. Alternatively, leave a small clearance underneath when fitting. Do not push the end of the pickup pipe flat against the bottom.
5. Slightly rotate the elbow to provide additional space for inserting the pickup pipe at an angle. Then, turn the elbow so that the end of the pickup pipe moves closer to the bottom of the tank.

If the tank overflows, water and sediment is drawn from the bottom region of the tank into the pickup pipe, then it moves upward to the overflow fitting and exits through the external overflow pipe.

The air vent stops the overflow pipe from turning into a continuous siphon, which would keep draining the tank after rainfall ceases.

Step 12: Position Tank, Connect Overflow Hose and Water Inlet

Locate the wheelie bin water tank near the rooftop collection point, such as a stormwater downpipe.

The overflow should be directed to a safe location that can handle heavy rainfall. The simplest solution is to channel it into the lower part of the stormwater downpipe directly below the collection point, which is its usual path when there is no water collection system.

It can also be directed into a garden, orchard, rain garden or a filter bed system that leads into a pond. From a permaculture perspective, overflow water is still a useful resource, so rather than sending it straight off the property, it can be directed through the landscape and put to further use. The overflow can feed a swale, infiltration basin, rain garden or heavily mulched tree basin, where the water spreads out, slows down and soaks into the soil.

In an orchard, overflow can be directed through shallow basins or swales around fruit trees, increasing the amount of rainfall stored in the root zone. On sloping sites, a series of connected swales or basins can allow water to overflow from one area into the next, progressively distributing it across the landscape. This follows the permaculture principle of slowing, spreading and soaking water, using the soil itself as an additional water-storage system once the tank is full.

Another option is to direct the overflow through a reed filtration bed or constructed wetland before it enters a pond. The vegetation and filter material slow the water and trap sediment, while the pond provides the final storage point. In this kind of system, the same rainfall is used several times: first as roof water stored in the tank, then as overflow watering plants and recharging soil moisture, and finally as water stored in a pond.

The aim is to create a sequence in which water moves progressively from one useful storage or growing area to another, rather than treating tank overflow as waste water that simply needs to be removed.

The rainwater can be collected directly from a stormwater downpipe, or from a rainwater diverter fitted to the stormwater downpipe.

In the images below, I show how I’ve arranged the tank. I attached a flexible 40mm agricultural pipe (also known as Ag pipe or Aggie pipe – the non-perforated type without holes!) to a rainwater catcher/first-flush diverter. The end of the 40mm Ag pipe simply sits inside the inlet filter basket.

Here’s the whole assembly, from gutter to bin!

This stormwater pipe is fitted with a leaf-shedding rainhead, which uses an angled metal screen to intercept and deflect leaves, twigs and other larger debris carried from the roof and gutters before they can enter the rainwater collection system. Rainwater passes through the openings in the screen and continues down the pipe, while most larger debris is shed from the outside of the rainhead rather than accumulating inside the pipe or being washed into the tank.

Removing this material before it reaches the tank reduces the amount of organic debris that can settle and decompose in the stored water, and also reduces the likelihood of inlet pipes, first-flush diverters and tank screens becoming blocked. The screen should still be inspected and cleaned periodically, particularly where the roof is surrounded by trees or receives large amounts of leaf litter.

A leaf-shedding rainhead is a coarse pre-filter, not a substitute for a first-flush diverter. It removes larger material, while the first-flush diverter captures the initial roof runoff containing finer dust, dirt, bird droppings and other contaminants that can pass through the rainhead screen.

This flows into a first-flush diverter, which captures and diverts the first runoff from the roof at the beginning of a rainfall event. This initial runoff usually carries the greatest amount of accumulated dust, bird droppings, leaf litter and other debris washed from the roof and gutters, so diverting it prevents much of this material from entering the water tank.

Once the first-flush chamber has filled, subsequent cleaner rainwater continues through the pipe to the tank. Many first-flush diverters slowly drain the captured water through a small flow restrictor after the rain has stopped, automatically resetting the chamber for the next rainfall event. The drain hole or flow restrictor needs to be checked and cleaned periodically because fine debris can block it. Australian Government guidance gives around 10 litres of first-flush diversion for every 50 m² (538 ft²) of roof catchment as a typical sizing guide, although the appropriate volume can vary with roof conditions and local requirements.

How Quickly Will a 220-Litre Tank Fill?

Even a small roof can fill a wheelie-bin tank surprisingly quickly.

A useful rainwater calculation is:

1 mm of rain falling on 1 m² of roof produces a theoretical maximum of 1 litre of runoff.

For example, a small 20 m² (215 ft²) shed roof receiving 10 mm (0.4 in) of rain receives:

20 m² × 10 mm = 200 litres

before allowing for losses.

That is almost enough rainwater to fill a 220-litre wheelie bin from empty.

A 20 mm rainfall event on the same roof represents approximately 400 litres of water, meaning roughly half the roof runoff would have to pass through the overflow if the tank began empty.

This demonstrates why overflow capacity is important even on a very small rainwater tank.

Using Water from the Wheelie Bin Tank

The simplest way to use the stored water is by gravity through the tap.

Because a wheelie bin is not very tall, the water pressure from the tap is fairly low. It is generally adequate for filling watering cans and can provide a slow flow through a short hose to a lower part of the garden, but it should not be expected to perform like a mains-pressure garden tap.

Elevating the tank increases the gravitational pressure but also creates a significant structural load on whatever is holding it up. Any stand supporting several hundred kilograms of water must be designed accordingly. It is not practical to elevate water tanks to increase pressure, as the height required to achieve a significant increase in pressure is not practical.

For a small garden system, leaving the tank at ground level is usually the simplest arrangement. Even with the tap close to the ground, a short length of hose attached to the tap makes it easy to fill watering cans or buckets, or to run a length of hose on fairly level ground to a nearby garden bed.

In summary, this covers the setup of a basic water harvesting system to start collecting rainwater. As shown in the instructions, it can be kept simple or made more elaborate. While a more complex system offers greater convenience, it also raises the setup costs.

The best advice is to start simple and expand it from there to suit your needs. This is likely the most efficient method and also the least intimidating.

To illustrate the point, here’s how my single wheelie bin system evolved into my current setup.

The small wheelie bin system shown served me effectively for over a year. Afterwards, I experimented with a modular, expandable setup using recycled plastic drums, which proved to be more affordable and durable than conventional wheelie bins.

The water storage system was expanded yet again. This is my water storage system today…

The wheelie bin water tank remains in use, positioned near the blue tanks (just outside this photo’s view), allowing me to pump in extra water as my storage fills up.

The six blue tanks have a combined capacity of 1320L (6 x 220L), and the wheelie bin adds another 220L, bringing the total to 1540L. This represents nearly 15% of my overall water storage, so it continues to contribute meaningfully to the system.

And it all began with a simple wheelie bin…

For more useful information on water harvesting, see the articles below:

• How to Make a Rainwater Tank from Recycled Plastic Drums
• How to Disinfect Your Rainwater Tanks if Something Falls In