The mesh has 5mm holes in it to allow the rain to enter the gutters however all the dust and other fine sediment that accumulates on the roof during the dry suddenly gets washed off and heads straight for the tank in the first few minutes of rain. This fine sediment will become an unwanted sludge in the base of your tank and lead to clogging of pipes. To remedy this I built a first flush diverter. Now you can buy a 90mm kit for $27 but where’s the fun in that! Also not everyone has access to a cheap kit but can easily make one up using regular plumbing fittings and following these steps.
There are recommendations of clearing 0.5-2L per m² but I would need either 30m of 100mm pipe or a barrel to do this. I figured even a small amount would help so I went about gathering the parts to build my DIY first flush diverter.
Generally a first flush system is connected vertically down from the main plumbing via a T-joint fitting. Since I was using 90mm pipe I needed the top part to be a short 90mm section to slot into the T-Joint. This went into a 90-100mm adapter. Even though it’s expanding into 100mm I used the word ‘reducer’ because when you go to the shops and ask it may be labelled as such. The reducer is important for two reasons. It allows me to use 100mm pipe which gives me an extra ~5.5L for every metre length. Secondly, by putting a 92-95mm wide float in the 100mm pipe the difference in diameter is how the float will plug up the diverter when it rises to the top to allow water to then head towards the tank. A 100mm sleeve/coupling is then used to attach the reducer to the 100mm section of pipe that will hold the dirty water. Note: The coupling at the top does not need to be threaded.