Connecting Two Rainwater Tanks

One of my goals for the year was to buy and install a third rainwater tank.  After a few good months of saving, I had enough to call up the tank manufacturer in Ballarat and order one.

We got it delivered a week before Easter, so as it was raining, I thought it best to connect it right there and then.  The connection was a shocking job, and I rushed it.  So I decided to redo it over the weekend.

The new tank is on the left.  Don’t ask me why we ordered a different colour.  Okay, I will confess.  During the ordering process, Kim and I were convinced that the original tank was the light green colour, and as it was dark and cold we didn’t bother to check.  Our bad, but not to worry because it still holds water and that is the main thing, isn’t it?

So on to the connecting business.

The dark green tank was already connected through to the irrigation systems, so I disconnected it all.

I have seen some people connect the tanks at the top through the storm water drain outlet, and this does work, however the light green tank is slightly higher than the original tank, so this method would not have worked (water doesn’t run up hill).

The only option I had was to connect at the bottom via two taps and some pipe.

I drilled a whole in the bottom, through the threaded hole, with a 22 mm spade bit.  The hole is 25 mm, so the smaller spade bit ensures that you don’t strip the thread away.  It is a fairly simple exercise, because there is a small guide hole for the tip of the spade bit.  I removed as much of the plastic waste as possible back through the hole.  I then lined the thread with teflon plumbing tape to stop any potential leaks via the thread, and screwed in the tap.

I then fitted a reducing thread to get it down to a workable 20 mm, which is the right size for most garden fittings.

With more teflon tape, it was ready to connect to the original tank.  Note; the water on the ground is from when I disconnected the two tanks to make these modifications.

Then I had to work out a way to balance the two tanks without all the water going into the garden.  I found an old tap in my box of tricks.  I think I recovered this when I unplumbed the original irrigation system when we first moved in.  I keep most things like this, because a) they are expensive to buy, and b) you never know when you are going to need one!  I fitted a T-piece that had a 20 mm thread, with two 19 mm barbs.

Then I pushed in two pieces of 19 mm poly pipe and clamped them.  I then measured the correct length for each pipe, then cut and connected to two 20 mm threads with barbs and clamped again.

It all lined up perfectly.  As you can see above, with the main line tap off, and the two tank taps on, it balances the water from the dark green tank to the light green one on the left.  The dark green tank is the one fed from the gutter, as I have only fitted one down pipe from the gutter.

This is just simply magical.  The yellow tap stops the water flowing down the main-line when balancing the water.

Just one word of caution.  This is not pressure pipe and should not be used for normal plumbing installations, as it may burst.  The water in the tanks is not under pressure, so this is a fairly safe setup.  Besides, when not in use, I turn off both taps on each tank.  I have only been balancing the tanks when it has been raining to avoid any issues.  If, some time in the future that I wanted to plumb this into the toilets or laundry, I would use a plumber, who would use the correct pipe.

So there you have it.  Two connected tanks, we have increased our water storage capacity by another 2100 litres, and not a leak in sight.  I am very pleased with my efforts.

As with any project, if I can do it, anyone can! Connecting two rainwater tanks is easy. Now I have to figure out how to reconnect all those small water barrels back into the system. I better get my thinking cap on.

Can anyone think of a good use for small 100 litre water barrels?