Thanks for the suggestions John
- use standard 90mm pipe, most fittings suit it and its less likely to block
In the USA where I am located pvc pipe is typically sold in 3" or 4" diameters. It looks like 90mm is just over 3.5". I can go with the a 4" pipe if the larger size is better to avoid blockages.
- fit a back flap to the pipe before the flow hits the first flush unit, it will stop air flow, but allow water flow.
A back flap would likely work better than a water P-trap. I hadn't thought about that possibility. I will investigate and see if I can find some type of flap that will open with water pressure but not air/wind pressure.
- why not run the water from the south side across the greenhouse to the discharge point outside.
I am not sure what you mean by outside. Nighttime temperatures here this week are at 5°F/-15°C and the winter temperatures here sometimes go down around -10°F/-23°C. Pipes with water outside the greenhouse can freeze and burst.
- would a larger tank be useful, the larger the cleaner the water
Yes a larger tank would be nice to have. I need to fit the tank inside my greenhouse to keep it from freezing and I would like to minimize how much planting space is lost to the tank. The 750 gallon/2839 liter tank I have been looking at has a 4 foot/1.2 meter diameter and a 8.8 feet/2.7 meters height which is low enough that I can drain water from a 12 foot/3.7 meter gutter into the tank. I will look around some more to see if there are any larger tanks available with either a 5 foot/1.5 meter or 6 foot/1.8 meter diameter which are still short enough to drain into from my gutters. The available choices for height and diameter combinations of the tanks I have found are somewhat limiting.
