Thread: Connecting multiple tank overflows into stormwater

I have three water tanks side-by-side (2 x 4000g; 1 x 2000g)…just had a new one delivered. The larger tanks have 2 x 90mm overflows, while the 2000g tank has a single 90mm overflow. I am wanting to connect all these overflows to a single stormwater line, which will run past all the tanks and then out to the garden (rural property, no stormwater system to connect to). <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
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My questions are:<o:p></o:p>
o Could I get away with a 90mm stormwater line or should I increase the size to, say, 100mm? I want to avoid any possibility that the overflows might back up in a storm situation (in the past, I had two tanks feeding into a 100mm line & had no backup problems…I found the gutters tend to overflow in a heavy downpour situation anyway, so not all the heavy rain makes it to the tanks).<o:p></o:p>
o Assuming that the 100mm stormwater line is best, what is the best way to connect the 90mm downpipes into the 100mm line? (I’m thinking a 90-100mm connector + a 100mm y-shaped junction to take the 2 x 90mm downpipes to a 100mm t-junction for each tank, so that when the 2 x 90mm downpipes flow together it will be in a 100mm pipe…the problem is that the 100mm fittings seem to be about double the price of 90mm).<o:p></o:p>
o Also, is there a difference between 100mm PVC pipe & 100mm sewer pipe? Is one thicker, are the fittings going to be more expensive?<o:p></o:p>