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How to Build a Self-Cleaning Rainwater Tank from a Wheelie Bin

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Wheelie bin as a water storage container

You can never have enough water storage, and a spare wheelie bin makes a handy water carrier that can easily be moved around (when it is empty of course, a full one can’t be moved!)

This design was my first ever water storage solution, and being rather experimental, I kept on adding to the design to constantly improve it,and this is the final result.

In case you’re wondering how this is any different to any other small water tank design, this one is actually self-cleaning. It has an inbuilt siphon to pick up sediment from the bottom and wash it out of the overflow outlet.

So, this is really two instructions in one – how to convert a wheelie bin into a water tank, and how to build a self-cleaning tank system that you can adapt to any tank system, so you can do either or both!

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“.

Design Theory

My intention with this project is to briefly take you through a simple water tank design, and then explain the construction of a basic self-cleaning system that removes sediment from the bottom of the tank automatically when the tank overflows. This self-cleaning design can be adapted to any water tank, including full sized commercial water storage systems.

In fitting in with the permaculture principle of having things serve more than one purpose, this design uses the one tank function (an overflow outlet) to achieve two purposes:

  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

Typically, overflow outlets sit high up near the top of the tank, so when they fill, the excess clean fresh rainwater coming in pours straight back out of the side of the tank, usually via a flexible pipe, to somewhere else where it may be utilised, and preferably, anywhere but the stormwater drain.

…if you think you have no more places to store water, consider the most obvious one that nature uses…

As an aside, if you think you have no more places to store water, consider the most obvious one that nature uses – your soil! Soil has a capacity to hold a considerable amount of water, so if your tanks are full and rain is coming, pump your tanks out into the soil, and let the rain refill them, rather than letting perfectly good stormwater go to waste. Unless you’re in one of the higher rainfall areas of Australia, you won’t have to worry about turning your garden into a swamp…

Now, the problem with traditional overflows is quite obvious, you end up dumping clean, fresh, oxygenated water that has just come in straight back out, while leaving the old, stagnant, anaerobic (oxygen-deprived) water sitting in the bottom of the tank with a thick layer of sludge and sediment, which makes for a nice breeding place for the less-friendly types of bacteria.

If the new fresh water could push out the old stagnant water as it comes in, and push out some of the dirt and sludge out with it, then this would be ideal! And that’s precisely what we’re doing here…

The diagram below shows how it works.

  1. Rainwater coming in causes the water level to rise. It cannot escape from the tank until it reaches the level of the overflow outlet.
  2. If the overflow was just a hole in the side of the tank, when the water level rises just above the level of the bottom edge of the hole, it would naturally trickle out from the top.
    By fitting a pipe (the “riser tube”) to the hole and running it to the bottom of the tank, we still have a hole in the side of our tank, only the water has just got a longer way to travel now to get out, from the bottom of the tank, all the way up.
  3. Now, when the water level rises in the tank, it rises an equal height in the riser tube. As soon as the water level inside the riser tube reaches the horizontal or level section where the hole is, it is sucked up from the bottom of the tank and flows out through the overflow pipe to the ground.
  4. The suction through the pipe works like an underwater vacuum cleaner and draws out the dirt and sediment out with the water at the bottom of the tank.

For anyone who has ever used a piece of tubing to siphon liquids from one container to another, this should look quite familiar. Without the air inlet at the highest point of the riser tube, it’s just one great big siphon. If you don’t include an air inlet, then once you get any water flowing the overflow, it will continue to flow out by itself until it empties all of the water! Believe me, it happened, and then I realised I needed to include a air inlet (a simple “T”-shaped fitting) to work as suction breaker to prevent automatic siphoning. This way, when the water level falls below the overflow outlet level, air comes in from the top via the air inlet and interrupts the flow of water. Simple, but effective!

Construction

The construction of this unit is fairly simple and straightforward, and you can build a basic water storage unit by completing only a few of the steps. The rest are optional, and can also be completed at any point in time to add extra functionality as desired.

Step 1 – The Bin!

Firstly, you will need a wheelie bin, either new or recycled, to hold the water.

Make sure that the bin is in good condition and has no crack or damage, as a full wheelie bin is rather heavy (220kg for a 220litre bin – water weighs 1kg per litre) and may burst if it is weakened.

You can really adapt this design to use whatever water container you wish.


Wheelie bin (220 litre unit pictured) or any other suitable container

Step 2 – Inlet Filter – Water In!

A medium sized 20cm aquatic basket pot (used in water gardens and ponds) serves as the water inlet filter.

This strains out any large debris, such as leaves, and prevents mosquitoes from getting into your water tank and breeding in there.


Medium size aquatic basket pot (20cm wide)

Step 3 – The First Cut

A hole needs to be cut into the lid of the bin to fit the water inlet filter (the aquatic basket pot). Use an electric jigsaw or any other suitable hand saw that can cut curves, such as a keyhole saw.

Note – the hole must be small enough so the pot cannot fall through! The pot has a wider lip, which will hold the pot up.


Cut-out made with jigsaw, smaller than the lip of pot

Step 4 – Fit Inlet Filter

Set the water inlet filter (the aquatic basket pot) into the hole in the lid.

It should be a nice snug fit with no gaps.


Basket pot set into wheelie bin lid

Step 5 – The Outlet – Water Out!

Now that we can get water into the bin, we need to be able to get it out too! To fit a tap of some sort to the tank you will need to use a 20mm threaded tank adapter, pictured below.


20mm Threaded Tank Adapter

Step 6 – Drilling Tools

To drill a precise hole that will be watertight with the threaded adapter fitted, you will need and electric or cordless drill and a holesaw as pictured below.

The outer diameter of the 20mm threaded tank adapter is 25mm, and this will make for a nice, snug fit.


Electric or cordless drill with 25mm holesaw

Step 7 – Mark Drilling Location

Mark where the hole is to be drilled on the wheelie bin – I have located mine 10cm (4”) above the bottom edge of the front, in the centre. You can choose to place the tap wherever you require it. If space is an issue, and you need clearance from the front, you can place the tap on the side, for example.

Step 8 – Drill Hole

Drill the hole at the location marked. If there are any rough edges after the hole has been drilled, smooth them off both inside and outside the tank with some sandpaper.

Step 9 – Fit Outlet

Fit the 20mm threaded tank adapter, and tighten it by using an two adjustable spanners, on on each side, that is, one inside the tank, one outside it. Tighten in reasonable but do not over-tighten.

Step 10 – Fit Taps

To turn the water on and off, you’ll need a tap or ball valve. The ball valve opens fully by turning the lever a quarter turn, it’s a nice convenience, but costs a lot more than a common garden tap, which will do just as well.

Make sure you check that the tap or ball valve screws into the 20mm threaded tank adapter when you purchase the parts – if they don’t you might need some additional fittings, so make sure you have these before you commence!

Ball valve (left) or Tap (right)

This is my completed outlet tap setup. I’ve added a few more fitting so I can connect a garden hose straight to the click-fitting on the end.


Ball valve fitted to threaded tank adapter

At this point, you have a tank with an inlet and a tap, it will collect and dispense water, and if you’re happy with that, then your project it complete!

Now, if you still wish to add a “few more bits”, then read on…

Step 11 – Fitting an Overflow

An overflow is simply another outlet placed higher up, on any one of the sides of the the tank, that lets excess water out when it reaches that level. It prevents water overflowing out of the top of the tank and flooding the surrounding area once the tank is full. By connecting a pipe to the overflow outlet, you can redirect the excess water where you want, back into a drain, to the garden or lawn, another tank, wherever you like.

Simply mark a spot on the side of the tank near the top, at the level where you don’t want the water to drain out. Then drill another hole at this point with the drill and holesaw, fit another 20mm threaded tank adapter, and screw on a 20mm elbow fitting (“L”-shaped) to point the outlet down. Add whatever fittings you need to connect your hose of choice.


Overflow fitted to side of drum (left) and flexible “washing machine” style hose connected to overflow outlet (right) (Pictures from previous project Recycled Plastic Drum Rainwater Tank )

If you’re happy with a basic overflow, which is what I use on my main water collection setup, then your tank ifs ready to go and “flood-proof” too!

But still, if you want to keep on going, there’s a few more things to do…

Step 12. Setting Up Self-Cleaning Function

The picture below shows the siphon cleaning system set up inside the wheelie bin tank. The overflow sucks water and sediment from anaerobic region at the bottom of the tank and flushes it out to the stormwater drain or elsewhere.

NOTE: in the picture below, the overflow on the left is capped off and turned upwards because the tank was disconnected from use temporarily and this is a preventative measure to stop mosquitoes getting in, and water sitting long term in the fitting and becoming stagnant – it is normally pointed downwards, with an overflow pipe connected to it, as shown in the rest of the photos below.


Self-cleaning siphon overflow to remove dirt and sediment from tank

To set up the overflow siphon:

  1. Connect a 20mm “T-piece” to the inside of the tank adapter as a suction breaker to let the air in so it doesn’t self-drain the whole tank.
  2. Fit a 90 degree or elbow join (“L”-shaped) to point the pipe to the bottom of the tank.
  3. Fit a long 20mm riser tube that reaches to the bottom of the tank(approx. 60cm long for a 220 litre bin) to the elbow join – you may need to cut it to length, and it’s OK if it sits at an angle, as long as it reaches the bottom.
  4. Cut notches in the end of the riser tube that rests on the bottom of the tank, as shown in the diagram below, to assist water flow and sediment collection while preventing blockage.


The riser tube rests against the bottom on the tank, and has slots cut into the end of it to improve flow and sediment collection.

Step 13 – Position Tank, Connect Overflow Hose and Water Inlet

Locate the Wheelie Bin water tank near your collection point, such as a stormwater downpipe.

If you haven’t connected an overflow hose yet, this is the time to do it!


Fully set up Wheelie Bin tank with siphon cleaning system and overflow pipe

You can collect the rainwater directly from a stormwater downpipe, or from a rainwater diverter that you have fitted to your stormwater downpipe.

In the pictures below, you can see how I’ve set the tank up. I have connected a flexible 40mm agricultural pipe (aka Ag pipe or Aggie pipe – the non perforated variety, that is without the holes!) to a rainwater catcher/first-flush diverter assembly. The end of the 40mm ag pipe just rests inside the inlet filter basket.

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

That covers the setup of a basic working system that will get you up and running with rainwater harvesting. As you can see from these instructions, you can choose to make it as simple or as complex as you choose. The complexity increases the convenience factor, but also escalates the setup costs accordingly.

The best advice is to start simple, and expand it from there to suit your needs. That’s probably the most efficient way to do it, and the least confronting too!

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

The little system you’ve just seen served me well for over a year, then I started experimenting further with a modular, expandable system, using recycled plastic drums, which were cheaper and more durable than wheelie bins.

As is visible on the right, the trusty wheelie bin still in service, though a little out of place.

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

The wheelie bin water tank is still in service though, it sits close to the blue tanks (just outside the view of this photo) so I can pump extra water into it when my storage is filling up.

The six blue tanks hold 1320L (6 x 220L) and the wheelie bin adds another 220L, taking the total capacity to 1540L. It accounts for almost 15% of my water storage capacity, so it still does its part in the grand scheme of things!

And to think it all started out with a wheelie bin…

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