Onion tanks are a collapsible flexible tank, which when filled, are self-erecting. Onion tanks are relocatable and lightweight, making them the perfect tank solution for remote locations and rapid deployment situations.

Flexitank offers the largest range of onion tanks available anywhere in the world.  With capacities ranging from 1200 litre (317 USG), to 120,000 litres (31,700 USG) there is not a purpose or an application that our onion tanks do not suit.

Onion Tanks are profile circular-shaped tanks with a self flotation collar made of closed-cell foam. Onion tanks are used for spill recovery, fire fighting, storage of oil, potable water, sewage, and other liquids.  Onion Tanks are very lightweight, reliable, fast response units requiring no setup. No frame is required as the floating collar rises automatically as the onion tank fills.

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Onion tanks are primarily designed for applications where rapid deployment is required with minimal set up time:

  • Collapsible water reservoirs for fighting fires and bushfires, especially helicopter refills
  • Foldable water storage for disaster or emergency relief
  • Potable (i.e. drinking) onion water tanks | emergency aid relief, potable mains water replacement
  • Food grade liquid storage
  • Water, fuel, and other liquids storage military onion tanks
  • Rainwater harvesting and rainwater storage
  • Collapsible water storage tanks for remote locations (e.g. mining camps, exploration and drilling operations)
  • Temporary onion septic tanks for wastewater, gray water, black water, and sewage storage
  • Temporary containment of almost any liquid (wastewater clean-up, oil spill, chemical spills, decontamination)
  • Onion water storage tanks for construction sites
  • Collapsible fuel tank for temporary containment of spills of oil, fuel and etc.
  • Storage of hazardous liquids and chemical
  • Fuel and chemical storage for emergency operations
  • Storage of liquids for hydraulic fracturing
  • Foldable water storage container for temporary storage for water during maintenance of permanent storage facilities (e.g. swimming pools, tanks, ponds etc.)
  • Temporary containment of liquids during decontamination operations
  • Temporary liquid storage for repairs and maintenance of another liquid holding device (tanks, swimming pools, ponds)
  • PVC collapsible water tank suitable for use as settlement tanks for turbid water
  • Liquid fertilizer storage tanks

Onion tanks are offered in an 20 standard sizes that cover almost any liquid storage application:

For open top onion tanks, add 120mm to the height for the filled height of the onion tank including the floating foam collar.

Please note closed top onion tank are available in capacities from 1,000 – 15,000 litre options only.

All onion tank dimensions are listed as standard sizes supplied from Flexitank’s exclusively sourced Aqualine 850gsm TPO polymer fabric.

Check out Flexitank onion tanks in action:

Onion tanks provide an array of advantages unique to this style of flexible tank:


Very quick setup time

Most Flexitank onion tanks take 1 – 4 people between 5 and 10 minutes to setup


No frame or parts to assemble

simply unfold the tank and begin filling


100% self-supporting


Easy to pack down and fold away

Flexitank Australia’s design incorporates a reinforced ground sheet which doubles as a carry bag


The nature and shape of a Flexitank Australia onion tank means they have the ability to fill and empty at a much faster rate than that of a pillow tank

Flexitank Australia’s design incorporates a reinforced ground sheet which doubles as a carry bag


By utilising a greater height than that of a pillow tank, and onion tank will typically use approx. 25% less ground space to achieve its desired capacity


Flexitank Australia’s unique heavy duty construction makes our range of onion tanks suitable for a large variety of unique and difficult applications


Can handle ground inclines of up to 10 degrees


Open top tanks are supplied with a full cover

This protects the liquid being stored from dust and contaminants, which is very important in potable drinking water applications


Closed top roll top onion tanks offer 100% contamination protection for the liquid being held as well as additional liquid security

a vital aspect when holding sensitive liquids


Manufactured by Flexitank Australia to defence specifications using the latest welding technologies

Onion tank ease of use

Our onion tanks are designed to fulfil the needs of field personnel. We have given careful consideration as to how the tank will be transported and used in remote areas. We also considered the time pressures on-field personnel setting up onion tank water storage in an emergency. Our onion tanks can be deployed in a very short time, usually only 10 to 15 minutes by one or two people.

The self-raising collar design allows the tank to be filled with minimal worker involvement. This collar enables the onion tank to expand as it is filled, and contain the water body without the need for an external frame. The floating collar of our onion tank lowers gradually when emptying while maintaining its stability.

Onion tanks are completely collapsible. Our onion tanks are lightweight, therefore, they can be folded neatly and easily for relocation and/or storage. Our open-top onion tanks can be turned completely inside out, making for easy cleaning, and every onion tank has a groundsheet that also doubles as a carry bag when it has been packed up.  

For more information on onion tanks, or to discuss any projects that you have in mind, please fill out the form below and our sales team will be in contact with you as soon as possible:

Carbon footprint onion tanks explored