First Flush
Diverters

• Improve stored rainwater quality
• Remove suspended and dissolved organic and inorganic fine particles
• Drain wet system pipes to prevent anaerobic fermentation and tannin leaching
• Reduce sediment build-up
• Reduce sediment load on post-tank pumps and filtration systems
• Protect household fixtures and appliances (ie. washing machines, toilet cisterns, etc.) by lowering sediment and tannin deposits
• Reduce nutrient load in your tank to limit anaerobic fermentation and algae growth
• Diversion volume easily custom built through use of standard pipes
• Only way to keep fine and dissolved particles out of your tank
• Automatic reset valve drains after rainfall events
• Comes in kit form
• Reliable seal and shut-off valve

What comes in my first flush diverter kit?

The exact components included in your first flush diverter kit will depend upon the product you order and are listed on each individual product page. (For product-specific information, visit the product page for your chosen first flush diverter via the links above.)

Where should I install my first flush diverter?

Your first flush diverter can be installed anywhere between your roof catchment area and your rainwater tank to isolate and capture the first “flush” of dirty water at the beginning of a rain event. You may choose to install smaller diverters to divert rainwater from each downpipe or you may choose to install larger diverters to divert rainwater from several downpipes.

How much water should I divert?

In areas with mild pollution (e.g. open fields, no trees, no bird droppings or animal matter, clean environment) you should divert 0.5 litres per square metre of roof (0.0125 gallons per square foot of roof). In areas with higher pollution (e.g. leaves and debris, bird droppings, animal matter/carcases, pollution) you should divert 2 litres per square metre of roof (0.05 gallons per square foot of roof). These formulas will help you calculate your total diversion volume or, if you’re using more than one first flush diverter, the volume of water you should divert in each device (which will depend upon the size of the roof area that “feeds” each diverter).

How long should my first flush diversion chamber be?

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. For product-specific information, visit the support page for your first flush diverter.
1 metre of 90mm pipe = 5.9 litres
1 metre of 100mm pipe = 8.8 litres
1 metre of 150mm pipe = 18.8 litres
1 metre of 225mm pipe = 45 litres
1 metre of 300mm pipe = 72 litres

Can I run two or more pipes into one first flush diversion chamber?

Yes. Just remember that you need to size your first flush diversion chamber based on the size of the roof area that’s upstream from your diverter. If two or more pipes (aka lines) feed into a single diverter, you should size your diversion chamber accordingly by considering the total roof area that feeds both pipes.

Which flow control washer (valve) should I use?

Your first flush diverter comes with a range of flow control washers (valves). Each washer has a different sized hole. The size of the hole determines the rate at which your first flush diversion chamber will empty. A smaller hole will create a slower flow rate and release less water during a rain event, while a bigger hole will create a higher flow rate and release more water during a rain event. (Blockages excepted, any size washer will eventually fully empty your diversion chamber after each rain event.) Washers with a smaller hole will become blocked sooner than washers with a larger hole. Choosing your flow control washer is therefore a trade-off – lower wasted water during rainfall means more regular maintenance, while moderate wasted water during rainfall means less maintenance is required. However, when choosing your flow control washer, remember that the volume of water flowing from the largest washer, which has a 2mm diameter hole, will still be insignificant when compared to the rainfall flow rate.

Which way should the ball seat be oriented?

Your diverter’s ball seat is like a funnel: \ /. The narrow end is installed facing down so it can be sealed by the black ball. (For detailed installation instructions, visit the product page for your chosen first flush diverter.)

How do I plumb the trickle feed outlet on my first flush diverter?

You can use 12mm irrigation tubing to plumb the trickle feed outlet to a location away from the diverter. eg. into a garden via a drip irrigation line or stormwater pit connected to an approved discharge point.

Does my First Flush In-Ground need to be installed on/with a fall?

Yes. Your First Flush In-Ground must be installed on a fall for two reasons. First, so the water will drain completely from the chamber, and second, so the black float ball can find its way to the seat and seal the chamber. We recommend a minimum fall of 5 degrees. (For detailed installation instructions, visit the First Flush In-Ground Product page.)

5 degrees = 8.75% = 1 in12 (approx.)

If a diversion chamber is 2m long it will need to have 175mm of fall?

Minimum possible grade of 100mm stormwater drain shall be 1% or 1 in 100 the same 2m long diversion chamber at this grade would have 20mm of fall.

Can I use my First Flush In-Ground to drain my wet system?

Yes. Installing your First Flush In-Ground at the lowest point in your wet system will allow your system to drain completely in between rain events.

How do I clean my first flush diverter?

Slowly unscrew the black hose fitting from the bottom of your first flush diverter. If the diversion chamber is full of water, take care as the water empties. Remove the plastic filter (it may come out when you remove the black hose fitting) and wash under clean water. Check the flow control washer for any blockages and wash with clean water, then replace all these parts. (For product-specific maintenance instructions, visit the Product page for your chosen first flush diverter.)