Tank Overflows | Rain Harvesting by Blue Mountain Co


Effectively manage overflowing water and make it easy to connect standard plumbing fittings to your tank with our tank overflows. All our overflows can also be paired with mosquito proof screens or flap valves, and some can be used to increase your tank’s rainwater storage capacity.

With their curved 90 degree bends, our high level tank overflow outlets significantly boost the volume of rainwater you can store, giving you an added litre for every extra millimetre of water over a square metre. Choose from bend, high flanged or extra high flanged.

Product Families
90° Tank Overflow Bends
90° Tank Overflow Bends
90mm or 100mm
Tank Overflow Standard<br>(Corrugated Tanks)
Tank Overflow Standard
(Corrugated Tanks)
90mm M or 100mm M
Tank Overflow Standard<br>(Flat Wall Tanks)
Tank Overflow Standard
(Flat Wall Tanks)
5 Sizes
Tank Overflow Extra High Flanged
Tank Overflow Extra High Flanged
Tank Overflow High Flanged
Tank Overflow High Flanged
90mm or 100mm


  • Benefits of Tank Overflows
    • Allows you to effectively manage overflowing water
    • Allows you to fit standard plumbing fittings to your tank
    • Option to easily increase your tank’s water storage capacity
    • AS4020 compliant
    • Range of sizes and types to suit different tanks and stormwater pipes
    • Also available in kit form
  • Tank Overflow FAQs

    My tank is overflowing at the inlet rather than the outlet. What should I do?

    1. Check that your tank screen is free from debris, ie. leaves, sediment
      Your tank outlet may be restricted by a blocked Mozzie Stoppa or another obstruction.
    2. Check your overflow outlet for the presence of an obstruction and remove.
    3. Alternately, the level of your tank overflow may sit above the base of your tank inlet.
    4. Check that the outlet pipe is equal to or greater than the combind capacity of the pipe feeding your tank inlet
    5. If a Mozzie Stoppa is installed, remove, inspect and clean if necessary before reinstalling it at the outlet or replacing with a Mozzie Stoppa Easy-Clean.

    If your inlet/overflow issue persists, remove your tank screen and check for floating debris on the water surface. Floating debris such as sworf from the tank installation process’ may be blocking the Mozzie Stoppa during overflow and drifting away from the overflow when overflow has stopped.

    Should I choose a regular tank overflow or a high level product?

    High or extra high tank overflows offer a simple and effective way to increase your tank’s storage capacity.

    Whichever tank overflow product you choose to use, your overflow needs to sit below the base of your tank inlet screen. The advantage of the high level overflow is that it raises the maximum water level within the tank.

    What size should I choose?

    The diameter of the overflow must be equal to or larger than the diameter of the inlet pipe.

    Do I need silicon to seal my overflow to the tank?

    You can choose to use a gasket or silicon to seal your overflow to your tank. Silicon is not required if you use a gasket. All our tank overflow kits come with a gasket.

    Do I need a gasket to seal my overflow to the tank?

    You can choose to use a gasket or silicon to seal your overflow to your tank. A gasket is not required if you use silicon. All our tank overflow kits come with a gasket.

    Which way should I orient my high level overflow?

    The bend on your high level tank overflow should face up towards the top of your tank in order to increase your tank’s storage volume and overflow height.

    Can I install my high level overflow sideways?

    Yes. We recommend installing your high level overflow with the bend facing directly upwards, however, it can also be installed on an angle to adjust the upper level. This may be necessary to ensure the overflow level stays below the base of your tank inlet and/or tank inlet screen.

    How do I connect two tanks?

    When connecting two tanks, it’s best to connect them at the base with a balance line. It is important to ensure that the tank receiving water from the roof or other catchment area has an overflow outlet.

    Should I mosquito-proof my tank overflow outlet?

    Yes, it is important to mosquito-proof your tank outlet to keep mosquitoes and other pests out of your rainwater system. You can do this using a mosquito-proof tank outlet screen such as a Mozzie Stoppa Easy-Clean. All our tank overflow kits come with a mosquito-proof Mozzie Stoppa screen.

  • Photo Gallery

The Rain Harvesting steps addressed:

Learn more about applying the 8 Rain Harvesting steps.

Find out more

Rain Harvesting Design Service™

We'll design your Rain Harvesting system - for free!

Your selection

Add Rain Harvesting or Plumbing products to your list.