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Best way to change shed down pipes for small water tank

Hi guys,
we have a small garden shed with 75mm zinc downpipes. I like to change that setup so that I can join the two downpipes on one end and redirect the water into a small water tank.

Unfortunately Bunnings no longer carries 75mm PVC pipe fittings, and a zinc 90 degree elbow is a steep $45 – I'd need two of those, plus would need to work out how to solder connections. And the only rain harvester I found (I/N: 0276311) is for 90mm PVC pipes.

How could I solve this? Can I join zinc and PVC pipes? What harvester would work for 75mm? Or would I need to remove all and extend to 90mm (which will be overkill for the shed's water collection)?

Thank you!

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MitchellMc

Welcome to the Bunnings Workshop community @TheHandySqirrel. It's terrific to have you join us, and many thanks for your question about collecting rainwater.

You might like to draw a diagram of what you'd like to achieve, so our members better understand what you're working with. I'm sure they'll have plenty of great advice once they know exactly what's happening.

Unfortunately, rain harvesters are typically designed for more modern 90 PVC downpipe. You can connect similar-sized Zinc and PVC, and it would be best to add silicone to any joins before pop-rivetting them together.

Given the issues with trying to join Zinc to PVC and the lack of parts to suit your 75mm pipe, it might be best to swap over to a 90mm system even though it's going to be overkill for the job at hand.

Please let me know if you have any questions.

Mitchell

TheHandySqirrel

Thank you for the welcome @MitchellMc.

Here is a photo of the shed side:

There is another downpipe on the right, just behind the vertically stored timber. I want to join that one with the one in the foreground and then feed the water to the tank.

MitchellMc

It might be one of those situations where you need to have all the items in front of you to test the tolerances, but what do you think of this Holman 90 x 75 x 65 x 50 x 40mm Storm PVC Stepped Adaptor, @TheHandySqirrel? It's likely designed for 75mm PVC downpipe, but with pop-rivets and silicone, there's a good chance it could work. You'd need to cut your 75mm downpipe and have a stepped adaptor above and below the harvester. You'll also most likely need a length of 90mm pipe to join the stepped adaptor to the harvester.

Instead of joining the two downpipes, having a separate harvester on each downpipe could be less complicated given the lack of fittings. You could then run the hose from both harvesters into the water tank. In saying that, though, depending on the amount of rain in your area, you might find that just a single downpipe can keep that small tank topped up. It might be worth starting with the closer downpipe and adding the other side if it can't collect enough.

Mitchell

TheHandySqirrel

Hi Mitchell,

I like the idea of using and riveting together the existing zinc downpipes (I love recycling existing material). I found another post where Eric explains the procedure of connecting a 90mm PVC pipe to a zinc downpipe pop.

So my plan of action could be:

Cut the existing 75mm downpipes with enough length to rivet on 90mm downpipes
Use 90mm PVC pipe and fittings to do the corners and joining, then
Add the 90mm harvester.

The only thing I'm not sure about is how to bridge the air gap between the 75mm zinc and 90mm PVC pipes. Eric said that the "air gap between the pipe and the pop [is] preventing an air-lock from forming and causing your gutter to overflow", but if there is an air gap how would the two different tubes be joined? Wouldn't I need some kind of sleeve, or maybe the reducer you've mentioned?

Regarding rivet gun and rivets, would these be ok to use for the job?

Thank you for your help!

Jason

Hi @TheHandySqirrel,

Just wanted to let you know that Mitch is enjoying a well-earned break until Friday. @EricL will be back on the site to assist you tomorrow. Please let us know if you need any urgent assistance and we can tag other members for you.

Jason

EricL

Hello @TheHandySqirrel

Thanks for sharing your question about your downpipes. One other option is to let some of the 75mm pipe travel inside the 90mm so that you don't have to use a reducer to join them together. I've placed an example of how you can join your downpipes together to allow you to combine the flow into one outlet. I've also placed the Rain Harvesting 90mm Leaf Beater Rain Head as close as possible to the water tank for easy cleaning.

The air gap is usually a gap between the gutter and the pipe itself, it's around 10mm and the general rule is that the downpipe must not be glued to the bottom of the gutter. In order to hold the downpipe in place, I suggest using Kinetic 90mm DWV Pipe Saddle Clips.

Please note that the layout is an example only and I suggest modifying the downpipe to your needs.

If you have any other questions, please let us know.

Eric

TheHandySqirrel

Hi Eric,

thank you for taking the time to illustrate your solution. That looks good, and I think switching to 90mm pipes overcomes a lot of hard-to-get 75mm fittings.

I now have a much clearer picture of how I'll solve this one.

Thank you!

EricL

Hi @TheHandySqirrel

I'm glad my recommendations have given you an idea of how to proceed with your downpipe project. Please make sure to post an update once you've finished with your modifications. I'm sure our members would be keen to see what it looks like.

Eric

MikeTNZ

Hi @EricL,

Thanks for mentioning DWV pipe, (for those that don't know, these are Drain, Waste, Vent pipes that are thinner than normal pressure PVC pipes).

And these can be used for installations like rain water collection, without the cost of using pressure pipe.

You will still have to use solvent cement to hold any joints you make in the pipes together, but if you use the yellow Marley stuff, you should be all right.

Just a note to anyone who is going to harvest water from their roof, this is not potable water, as in not drinkable, you may have bird effluent on your roof as well as possible lead-head nails holding the roofing sheets down, please do not drink any water that comes off of your roof, without prior treatment.

Birds carry salmonella among other things, lead poisioning is a slow death.

Just be aware of the risks.

Cheers,

Mike T.

TheHandySqirrel

Hi Eric,

I have now installed the pipe and harvester. Instead of the suggested saddle clips I used 20x600mm Make-a-Bracket. Each strip gave me two brackets bringing down the cost to just $1 per bracket. As this is the back of our plot there was no need for a polished look.

Images below. Now I'm just waiting for some rain (which shouldn't take long these days).

The final installation.

Detail of a bracket and the outlet where I repurposed an old dishwasher pipe.

MitchellMc

That looks fantastic, @TheHandySqirrel! Well done on overcoming a difficult situation and constructing an effective solution.

Many thanks for updating us on your success. I can't wait to see what project you tackle next.

Mitchell

EricL

HI @TheHandySqirrel

Thank you very much for the update. Your downpipe upgrade looks great and excellent spotting on those 20x600mm Make-a-Bracket. That's an excellent bargain for a bracket.

We look forward to seeing your next project.

Eric

Rayser

Hi @TheHandySqirrel

I have a job similar to your design above.

My joints are firmly in place by pushing them together and I do not get any leaks.

Is it necessary to glue all joints?

MitchellMc

Welcome to the Bunnings Workshop community @Rayser. It's brilliant to have you join us and great to see you jump into the discussion.

In a non-pressurised system like collecting rainwater into tanks, glueing every joint might not be required. However, it's extremely simple and quick to do; not only does it prevent leaks, but it also adds rigidity to the joints. There's no real reason not to do it.

I'm keen to hear all about your projects and plans around the house and garden. Feel free to reach out anytime you need assistance or have something to share.

Mitchell

TheHandySqirrel

Hi @Rayser,

as usual, "it depends". For my drainage installations I have glued all connections as I didn't want to take the risk of one part moving and then dislocating a joint, causing a leak. Over time, things might shift even if they don't look like they'll do now.

In another electrical installation I didn't glue the parts, and in hindsight I think I should have. Although this makes it very hard to alter anything, it would give me peace of mind that there wouldn't be any water ingress potentially causing shorts.

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