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Wet-Dry Valve

Wet-Dry Valve
Automatically drain your charged lines after it rains using our wet-dry valve and prevent problems with tannin leaching and anaerobic fermentation.
Size 100mm WDAC21

Drain your pipes

For ‘wet’ Rain Harvesting systems, it is important to drain your charged lines after it rains to remove any water remaining in the pipes.  Draining this water prevents it from becoming stagnant and discoloured due to anaerobic fermentation and tannin leaching – and most importantly, stops it from being fed into your rainwater tank at the next rainfall event.

Set and forget

The Wet-Dry Valve’s electronic auto-release timer allows you to set the frequency at
which your charged lines are drained.

Benefits of the Wet-Dry Valve

For ‘wet’ Rain Harvesting systems, the wet-dry valve makes draining charged-lines (water-filled pipes) easy.

The valve’s drain size allows for efficient draining and minimises the risk of clogging.

Customise the settings on the Wet-Dry Valve’s electronic auto-release valve to ensure your charged lines are drained.

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

  • Installation
    1. Select an installation point for your Wet-Dry valve. This should be at the lowest point in your wet or “charged” system. Your wet-dry valve and pipe work should be installed on a slope to ensure it drains correctly. The valve must also be accessible for maintenance and inspection. This may be achieved by running pipe to a location above ground or installing in an access pit (e.g. stormwater pit).
    2. Using an appropriately sized T-junction, as a template, measure the pipes at your chosen installation point and cut to create space for the T-junction. If the lowest system point is located at the existing 90 degree bend in the pipe that feeds your tank, the T-junction can be used in place of the existing 90 degree bend to direct water vertically to the tank. Otherwise the T-junction can be installed in your existing horizontal pipework. Whichever installation option you choose, ensure all cut edges are clean and smooth.
    3. Install the T-junction using solvent weld glue.
    4. If termination is below ground level, extend outlet of T-junction to nearest stormwater pit and through pit wall. If outlet is to be terminated above ground, extend outlet of the T-junction to the sloping ground where pipe work becomes accessible.
    5. Apply solvent weld glue to the 100mm end coupling socket and external section pipe end. Push on end coupling and hold in position until the glue sets. Ensure the tapered section of the coupling faces up to allow all water to escape when draining.
    6. Attach the clear conical cone to the threaded coupling ensuring the O-ring seal is in place.
    7. Attach the wet-dry valve by first installing the 25mm x 20mm reducing adaptor and washer to the 25mm thread of the clear conical end cap. Remove the union from the valve and attach to the reducing adaptor with 20mm washer in place. Attach the valve at the union and orientate dial for easy access.
    8. Ensure all subsurface pipe work has been backfilled and supported correctly using appropriate bedding sand or similar after testing for leaks.
    9. Remove the waterproof cover from the wet-dry valve and carefully slide out the battery box. Install two new 1.5 volt AAA batteries, then replace the battery box and waterproof cover.
    10. Test the unit by turning the drain time on and then off. You should hear the sound of the motor within 30 seconds. If you do not hear the sound of the motor, check that the batteries are installed correctly.
    11. Set to the required opening intervals and opening duration.


  • Maintenance

    It’s important to ensure that your wet-dry valve outlet remains clear of any debris. If your outlet becomes blocked, the chamber will not empty and the wet system of water will not drain down.

    To ensure the flow of water out through your wet-dry valves outlet, periodically check the transparent conical end cap for any build-up of matter. Remove and clean the conical end cap if required.

    Periodically check that the wet-dry valve batteries have charge. This is indicated by the flashing light.

    To prevent your wet-dry valve from freezing or “winterising”, remove the timer prior to the first frost or freeze and store it indoors until spring. Remember to remove the batteries from the battery compartment.

    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 wet system and wet-dry valve.

  • What's in the box?
    • 100mm multi-fit threaded coupling
    • 90mm clear conical cone
    • 25mm x 20mm reducing adaptor
    • 25mm washer
    • 20mm washer
    • Auto-release timer



  • Tools you might need
    • 100mm pipe (for extension to valve location)
    • 100mm T-junction
    • 100mm various fittings (for extension to valve location)
    • Tape Measure
    • Marker pen
    • Saw
    • Solvent weld glue
    • Bedding sand or similar
    • 2 new 1.5 volt AAA batteries
  • Product FAQ's
    • 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.

Products you may be interested in

First Flush Advanced
First Flush Advanced
Leaf Eater Original
Leaf Eater Original
90mm or 100mm
Maelstrom Filter
Maelstrom Filter

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