4" First Flush Diverter

Calculated at Checkout

Product Overview

" First Flush Plus Diverter

Protect your rainwater quality by diverting the most contaminated water that washes off your roof with the first few inches of rainfall using the Rain Harvesting First Flush Plus.

First Flush Plus Tee Resized


Supplied in kit form, the first flush diverter can be installed on your downpipes with a simple T junction. Simply add and install the length of pipe required to meet your diversion needs. This will be based on the volume of dirty, contaminated water you wish to divert.

First Flush On Blue Tank Next To Vege Patch


Help prevent hazardous organic and inorganic particles from contaminating your rainwater by diverting and discarding the most particle-laden water from your roof. This first flush diverter captures the first flush of rainfall so you get better quality water in your tanks.

End Cap With Flow Controllers FF


The water you divert is automatically released through the slow release valve. You can empty this water into a standard drip irrigation system for use around your garden or you can direct it into storm water drainage. The choice is yours.



1. First Flush Plus Tee

2. Ball Seat

3. End Coupling

4. Pipe Wall Brackets x2

5. Sealing Ball

6. Transparent, Rapid Release, Exit Funnel

7. Flow Control Valves x8

8. Plastic Filter Screen

9. Hose Connector


Calculate your diversion needs 

Generally speaking, the more water you divert, the better the quality of the rainwater that ends up in your tank. However, diverting more rainwater than necessary can lead to volume shortages, so it’s important to calculate your diversion needs, and divert water accordingly.  

The following formulas offer general guidelines for calculating how much water you should divert: 

  • Areas with low pollution (open fields, no trees, no bird droppings or animal matter, clean environment) = divert 0.5 litres of water per square metre of roof 
  • Areas with higher pollution (leaves and debris, bird droppings, animal matter/carcasses, pollution) = divert at 2 litres of water per square metre of roof.  

This calculation will allow you to determine what length and size pipe or pipes you need for your diversion chambers.

The length of pipe required to form your first flush diversion chamber will depend upon how much water you need to isolate and capture. The following measurements are given as a guide only.

1 metre of 90mm pipe = 5.7 litres
1 metre of 150mm pipe = 18.8 litres
1 metre of 300mm pipe = 72 litres
3 feet of 4″ pipe = 2 gallons
1 metre of 100mm pipe = 8.8 litres
1 metre of 225mm pipe = 45 litres
3 feet of 3″ pipe = 1.5 gallons
3 feet of 12″ pipe =19 gallons

First Flush diverters help you plan for volume by allowing you to choose your catchment volume with custom catchment size and/ or an advanced release valve.

First Flush Diverters help divert the first flush, through their design. They are installed using a T junction or high flow inlet to which the diversion chamber is fitted. As the chamber fills with the initial dirty water from your roof, a ball rises until it seals the inlet, allowing the rest of your rainwater, which is much cleaner, to flow directly to your tank.