First Flush Diverter | Post, Wall & Stand Mounted | Rain Harvesting

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Kit
90/100mm (inlet only)
300mm Chamber
Steel Stand

First Flush Post/Wall

First Flush Diverters
A large and versatile unit that can be mounted in different places to keep highly contaminated water out of your tank.
Size 90/100mm (inlet only) WDPW01
Size 300mm Chamber WDAC09
Size Steel Stand WDAC01
  • 90/100mm (inlet only)
  • 300mm Chamber
  • Steel Stand
Green Tank With Green Post Wall First Flush

Protect your rainwater quality

By preventing the dirtiest and most hazardous water from entering your rainwater tanks, this first flush diverter protects your rainwater quality. The dirty water is collected at the beginning of each rainfall event and automatically drains away afterwards.

WDPW01 02 Kit New Primary Filter Screen

Install with ease

This versatile first flush diverter unit can manage water from single or multiple pipes. Wall, post and stand mounting options plus an all-parts-included kit mean installation couldn’t be easier. Simply add an appropriate length of pipe to divert as much as 150 litres as required.

 

WDPW01 Side 01 Resized

Divert larger volumes

The First Flush Post / Wall is larger than many residential above ground first flush diverters, allowing you to divert more water. This makes it particularly appropriate for buildings with larger roof areas or places with heavy pollution and overhanging vegetation.

 

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.

Learn more about the 4 pillars of designing a Rain Harvesting system. 

The Rain Harvesting steps addressed:

Limit sources of contamination     Plan for volume

Filter leaves and debris                    Divert the first flush

Secure the system                             Manage standing water

Consider a safety net                        Monitor and maintain

  • Specifications

    First Flush Post Wall Dimensions

  • Installation

    Wall & post mount

    1. Screw your wall/post bracket to the wall at your chosen installation point. The outlet of your diverter must sit at least 150mm from the ground when fully assembled. The wall/post bracket supports the lowest end cap of your chamber so select your installation point and attach the wall/post bracket accordingly.
    2. Screw your wall/post bracket to the wall at your chosen installation point. The outlet of your diverter must sit at least 150mm from the ground when fully assembled. The wall/post bracket supports the lowest end cap of your chamber so select your installation point and attach the wall/post bracket accordingly.
    3. Attach the upper and lower end caps to your 300mm pipe by applying solvent weld glue to the socket and pipe before inserting the pipe into the end cap and holding until the glue sets. Repeat for the other end cap. Expect a tight fit.
    4. Place your assembled diversion chamber in the wall/post bracket and support as you fit your upper bracket around the inlet on the upper end cap and screw it to the wall/post.
    5. CAUTION: Failure to support the unit in the upright position while attaching the upper bracket could crack the bottom chamber cap.
    6. Select the appropriate flow control washer and fit it into the hose connector with the side marked “TOP” showing. Start by using the Control Washer with the smallest gauge hole (lowest number). Try a larger gauge Washer if experiencing blockages. Save the remaining washers for possible future use.
    7. Insert the plastic filter screen in through the base of the screw cap with O-ring seal and secure by attaching the hose connector and flow control washer.
    8. Apply solvent weld glue to the socket of the threaded coupling and one end of the 90mm length of 90mm pipe. Insert the short section of pipe into the socket and hold until the glue sets. Insert opposite end of this short section inside the lower end cap outlet after applying solvent weld glue.
    9. Insert your Primary Filter Screen in the lower end cap, then attached the screw cap with O-ring seal (and assembled components) to the threaded coupling.

      NOTE: For some end couplings you may be required to remove and discard the molded keeper ring from the bottom of the Primary Filter Screen.

    10. Place the ball inside your first flush diverter chamber through the upper end cap inlet.
    11. Measure your existing downpipe and cut to create space for a T-junction. Ensure all cut edges are clean and smooth.
    12. Insert the ball seat into the top of the upper end cap inlet, with the narrow end of the seat facing down.
    13. If you’re fitting your diverter to a 90mm T-junction, cut a length of 90mm pipe to connect your diverter and T-Junction. Attach the pipe hard down on top of the ball seat, then attach the T-Junction hard down on top of the pipe.
    14. If you’re fitting your diverter to a 100mm T-junction, attach the 30mm length of 90mm pipe hard down on top of the ball seat and glue in place using solvent weld glue. Fit the T-junction around the upper end cap inlet or, if required, connect the T-junction and upper end cap inlet using an additional length of pipe.
    15. Connect the T-junction to the existing downpipe using solvent weld glue.

    Stand Mount

    1. Determine the length of 300mm or pipe required for your first flush diversion chamber using the table below and cut accordingly. Ensure all cut edges are clean and smooth.
    2. Attach the upper and lower end caps to your 300mm or pipe by applying solvent weld glue to the socket and pipe before inserting the pipe into the end cap and holding until the glue sets. Repeat for the other end cap. Expect a tight fit.
    3. Place your assembled diversion chamber into the stand, being sure to line up the centre of the chamber outlet with the weld on the stand.
    4. Select the appropriate flow control washer and fit it into the hose connector with the side marked “TOP” showing. Start by using the Control Washer with the smallest gauge hole (lowest number). Try a larger gauge Washer if experiencing blockages. Save the remaining washers for possible future use.
    5. Insert the plastic filter screen in through the base of the screw cap with O-ring seal and secure by attaching the hose connector and flow control washer.
    6. Apply solvent weld glue to the socket of the threaded coupling and one end of the 60mm length of 90mm pipe. Insert the short section of pipe into the socket and hold until the glue sets. Insert opposite end of this short section inside the lower end cap outlet after applying solvent weld glue.
    7. Insert your Primary Filter Screen in the lower end cap, then attached the screw cap with O-ring seal (and assembled components) to the threaded coupling.

      NOTE: For some end couplings you may be required to remove and discard the molded keeper ring from the bottom of the Primary Filter Screen.

    8. Place the ball inside your first flush diverter chamber through the upper end cap inlet.
    9. Measure your existing downpipe and cut to create space for a T-junction.
    10. Insert the ball seat into the top of the upper end cap inlet, with the narrow end of the seat facing down.
    11. If you’re fitting your diverter to a 90mm T-junction, cut an appropriate length of 90mm pipe to connect your diverter and T-Junction. Attach the pipe hard down on top of the ball seat, then attach the T-Junction hard down on top of the pipe.
    12. If you’re fitting your diverter to a 100mm T-junction, attach the 12mm length of 90mm pipe hard down on top of the ball seat and glue in place using solvent weld glue. Fit the T-junction around the upper end cap inlet or, if required, connect the T-junction and upper end cap inlet using an additional length of pipe.
    13. Connect the T-junction to the existing downpipe using solvent weld glue.
    14. Securely bolt the stand and check to ensure that the pipework connected to the top of your First Flush Post/Wall is stable and the unit is not stressed by misalignment.
  • Maintenance

    It’s important to ensure that your first flush diverter outlet remains clear of any debris. If your outlet becomes blocked, the chamber will not empty and the first flush of water will not be diverted when it rains.

    To ensure the flow of water out through your diverter’s outlet, periodically unscrew the outlet to allow debris to fall out. If the diversion chamber is full of water, take care as it empties. Remove the flow control washer, hose connector, keeper ring and filter screens and hose down or wash the screens with clean water. Check the flow control washer for any blockages and remove and clean as necessary.

    For best results and minimal maintenance, we recommend installing rain heads such as our Leaf Eater rain heads on all your downpipes to limit the volume and number of leaves and debris that reach your first flush diverter.

  • What's in the box?
    • Wall/post bracket
    • Upper bracket
    • 2 end caps
    • Hose connecter
    • 8 flow control washers
    • plastic filter screen
    • Screw cap with O-ring seal
    • Threaded coupling
    • Plastic filter screen
    • Primary Filter Screen
    • Ball
    • Ball seat
    • 90mm length of 90mm pipe (for joining end cap and threaded coupling)
    • 30mm length of 90mm pipe (Ball seat ring keeper)
  • Tools you might need
    • 300mm/12” pipe (for diversion chamber)
    • Tape measure
    • Marker pen
    • Saw
    • Solvent weld glue
    • Screws
    • Screwdriver or drill
    • 90mm pipe and T-junction (for connecting to 90mm installation)
    • 100mm pipe and T-junction (for connecting to 100mm installation)
    • Anchors x3 (for stand)
  • Product FAQs

    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. 

    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/carcasses, 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.

    1 metre of 90mm pipe = 5.7 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 

    3 feet of 3″ pipe = 1.5 gallons  

    3 feet of 4″ pipe = 2 gallons 

    3 feet of 12″ pipe =19 gallons 

    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. 

    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. 

    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. 

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