Having depended on rainwater for many years I think there are better ways to improve the quality of water captured from a roof without buying a range of off-the-shelf products that cost quite a bit of money (The Shed, Issue No. 77).
Normally, if it’s all of the roof water being captured, the downpipes link up to one 100mm diameter pipe which will either surround the house underground or perhaps run through the crawl space. This pipe feeds up the side of the tank and into the inlet. The simplest way to ensure the first flush is diverted is to simply install a diversion valve in the pipe as seen in the picture of our tank. All I do is leave the valve open so if there’s just a small shower the water doesn’t go into the tank — during summer that’s most of the time. I keep an eye on the weather forecast and after a bit of rain I go out and shut the valve. It sounds like a hassle but I don’t find it is. It’s just part of being aware of the weather. The same idea could be used if it’s only one downpipe being tapped into.
Another tip is to make sure the waste pipe from the valve is a loose fit so it can easily be removed and the cap of the diversion fitting can be unscrewed. I do this from time to time to clean larger bits of crap that block the outlet. This would not be necessary if a rain head or some sort of gutter guard is used, which is what I would have next time.
I would also put the diversion valve lower down the side of the tank and use a much bigger one so all the water that sits in the pipes around the house can be flushed out from time to time. As for the calmed inlet and floating outlet shown in your illustration, these seem unnecessary if the first flush is diverted, plus if you need to get into the tank to attach them they would be very difficult to install.
Finally, I wouldn’t install the tank siphon the way it is shown — it looks very likely to drain the whole tank.
Thanks for your email, Carey. Most of the products mentioned can be easily made by any DIYer — you don’t have to purchase the kits. The siphon will not empty your tank — it has a hole to break the siphon once the water level gets to a normal level. The real advantage of the siphon is simply to take advantage of the fact that you will have to spill water anyway, so why not use it to make sure that the waste water comes from the base of the tank, where most of the sludge will be, not from the fresh input? — Jude Woodside, Technical Editor