Onion Tanks for Storage of Fire Fighting Water and Liquids

  • firefighting water filled collar tank placed on a ground sheet with fully opened top
Fleximake onion tanks are frameless, self-supporting “Onion” shaped tanks that are used for storage of water and other types of liquids. Onion tanks, also known as collar tanks, collar dams, onion bladder tanks and collapsible tanks, are ideal for liquid storage applications that require deployment of tanks in a very short time. Typically, Fleximake onion tanks can be set up by one or two people and be ready for filling in about 10 to 15 minutes. Our tanks are fitted with innovative, circular, self-raising and floating collar, which is made of closed cell foam, for easy filling. This makes Fleximake onion tanks the ideal choice for firefighting, drinking water storage for disaster relief, military operations, spill containment, pool repairs and other situations in need of short term storage. These collapsible reservoirs can be emptied and folded neatly for storage and transportation. Fleximake onion tanks are designed to be tough and made with heavy duty fabrics for on-going use and for longevity. Our tanks can be supplied with a top cover to prevent contamination from outside sources. We manufacture our onion tanks from the highest quality, strong, durable and heavy duty materials suitable for harsh environments in rural, commercial, mining and industrial applications. We have onion tanks manufactured from a range of different materials that are best suited to your water or liquid storage application.

We manufacture all our onion tanks in Australia. We here at Fleximake have the fastest and most sophisticated plastic welding machines in Australia. The modern tech, high speed machines bring us the capability to guarantee you a fast turnaround time regardless of the size of any onion tank. This also means that we can offer you the best onion tank prices as opposed to our direct competitors.


Onion Tank Videos


  • Collapsible water reservoirs for fighting fires and bushfires, especially helicopter refills
  • Potable (i.e. drinking) onion water tanks
  • Food grade liquid storage
  • Foldable water storage for disaster or emergency relief
  • Water, fuel and other liquids storage military onion tankse
  • Foldable water tanks for rainwater storage
  • Collapsible water storage tanks for remote locations (e.g. mining camps, exploration and drilling operations)
  • Folding water tanks for waste water, grey water, black water and sewage storage, temporary onion septic tanks
  • 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
  • Onion water storage tanks for construction sites
  • 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
  • PVC collapsible water tank suitable for use as settlement tanks for turbid water
  • Liquid fertilizer storage tanks
  • Key Benefits

  • Self-supporting and frameless
  • Quick to set-up and knock-down
  • Can fold easily and neatly, therefore takes up less space.
  • Special low profile design for higher stability
  • Minimal site preparations prior to deployment
  • Innovative self-raising floating collar for easy filling.
  • Suitable for filling either from bottom fitting or from top by hose(s), which is supported by floating collar
  • Handles are fitted on the outside of the tank to allow easy lifting and quick set up
  • Handles are fitted on the inside of the tank to allow it to be turned inside out for easy cleaning
  • Our onion tanks are constructed using heavy-duty, reinforced, coated fabric material for longevity
  • Fittings can be selected according to your requirements, including the fire authority specified fittings
  • Shock cord straps to hold the top cover (optional) firmly in place to minimize contamination and also to allow easy access and inspection
  • Our onion tanks are made of puncture, tear and abrasion resistant fabric materials
  • Ground sheet included for additional protection
  • Low maintenance, easy to clean and repair
  • Capacity and Dimensions
    Fabric Material Choices
    Why Choose Fleximake
    Reading Resources
    Capacity and Dimensions

    Standard Capacity Range

    Fleximake manufactures a wide range of standard onion tanks for various applications and is suitable for various liquids. This includes potable water, non-potable water, chemicals, fertilizers, fuels and oils. Details of our standard sizes of onion tanks for sale are listed in the table below.

    Model NoCapacity(Litres)Base Diameter D1 (mm) Top Diameter D2 (mm)Height H (mm)
    FMOT002 _ _ _ _2,000L1,900mm700mm1,000mm
    FMOT003 _ _ _ _3,000L2,300mm1,000mm1,000mm
    FMOT005 _ _ _ _5,000L2,800mm1,500mm1,000mm
    FMOT007 _ _ _ _7,000L3,200mm1,700mm1,100mm
    FMOT010 _ _ _ _10,000L3,700mm1,900mm1,250mm
    FMOT015 _ _ _ _15,000L4,400mm2,600mm1,250mm
    FMOT020 _ _ _ _20,000L5,000mm3,300mm1,250mm
    FMOT025 _ _ _ _25,000L5,500mm3,700mm1,250mm
    FMOT030 _ _ _ _30,000L6,000mm4,200mm1,250mm
    FMOT035 _ _ _ _35,000L6,400mm4,600mm1,250mm
    FMOT050 _ _ _ _50,000L7,500mm5,600mm1,250mm
    FMOT070 _ _ _ _70,000L8,800mm6,800mm1,250mm
    FMOT090 _ _ _ _90,000L9,900mm7,800mm1,250mm
    FMOT100 _ _ _ _100,000L10,500mm8,200mm1,250mm
    FMOT130 _ _ _ _130,000L12,000mm9,500mm1,250mm
    Note: _ _ _ _of the model number in the above table represents the code for the fabric material. These codes are shown in the table in “Fabric Material Choices for Onion Tanks” tab that details the fabric material selection. Example: Material code for RPVC 900gsm is P09N. Therefore, the model number for 30,000L onion tank made out of food grade RPVC 900gsm is FMOT030P09P

    Please click here to download general arrangement drawing of our standard onion tank.

    Custom Made Onion Tanks

    Fleximake can provide you a tailor made solution to perfectly fit your requirements. We can design and manufacture onion tanks to meet the required liquid holding capacity, type of fluid you need to store, fittings and accessories.
    The friendly team at Fleximake are always happy to help with your specific requirement for liquid storage solution. Simply fill the Enquire form below or give us a call on 1300 195 295. We’ll discuss your needs and deliver the perfect solutions to you on time.


    We can offer our onion tanks with almost any inlet & outlet pipe fitting type or size you require. Following are some of the common fitting types used for onion tanks.

  • Poly tank fittings with ball valves
  • Aluminium flanges
  • Stainless steel flanges
  • Camlock fittings
  • BSP UPVC valve with PP male coupling
  • Quick couple hose and adapter fittings
  • Storz firefighting fittings

  • If the fitting you need is not listed above, please contact us. We are happy to meet your requirement.

    Accessories and Options

  • Top Cover
  • A valise with carrying handles for transportation of the tank when folded.
  • We can print your logo on the onion tank
  • Supply of complete solution, including pumps and fittings
  • UV (Ultra Violet) treated fabric materials
  • Fire retardant (FR) treated fabric materials
  • If required, secondary portable spill containment bunds can be supplied with onion tanks for chemical, oil or fuel storage applications
  • Fabric Material Choices

    Fabric Material Choices

    We manufacture our onion tanks from strong, durable, heavy duty fabric materials suitable for harsh environments in commercial, mining and industrial applications. We have onion tanks manufactured from a range of different materials that are best suited to your application.

    The selection of fabric materials that are used for manufacturing our onion tanks are listed in the table below. We select the most economical material suitable for your needs considering liquid characteristics. Please download the datasheets for properties and fluid resistance guidelines of our industrial fabric materials.

    Fabric Material g/m2 (gsm)Suitable applications Data sheet and Fluid resistance guidelineFabric Material Code
    RPVC900Non-potable water, Certain chemicals, Certain oilsDownload datasheetP09N
    RPVC900Food Grade, Potable water(i.e. drinking water) Comply with AS/NZ 4020 standardDownload datasheetP09P
    RPVC1100Non-potable water, Certain chemicals, Certain oilsDownload datasheetP11N
    RPVC1100Food Grade, Potable water(i.e. drinking water) Comply with AS/NZ 4020 standard or equivalent international standardsDownload datasheetP11P
    RPVC1400Non-potable water, Certain chemicals, Certain oilsDownload datasheetP14N
    TPU960Potable water (i.e. drinking water) Comply with AS/NZ 4020 standard or equivalent international standardsDownload datasheetTPUP
    TPU1230Fuels, Oils, Certain ChemicalsDownload datasheetTPUN
    ER10001000Most chemicals, Certain oilsDownload datasheetER10
    If applicable fluid does not list in the above fluid resistance guideline datasheets or if the data is not clear to you, please contact us in order to select a suitable material for your onion tank.
    Why Choose Fleximake

    Robust, durable and stable

    Fleximake onion tanks are designed and manufactured to be robust, durable and stable. All the seams of Fleximake onion tanks are fusion welded using cutting edge plastic welding machines for guaranteed 100% sealing and for strength. The fabric materials used for our onion tanks are heavy duty, abrasion resistant, puncture resistant and high in tensile strength.

    Fleximake provides a protective ground sheet with our onion tanks to provide additional protection when deployed on rough surfaces. We design our onion tanks with a special shape and a low profile to ensure that the tank is stable and sturdy when filled. Fittings are firmly attached to the tank with a reinforced double-layer of welded fabric material to ensure that the port does not break out of the tank wall with use.

    Filled Onion tanks Onion tanks strength Onion tanks fitting

    Ease of Use

    We have designed our onion tanks to fulfil the needs of field personnel, giving careful consideration 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. The onion tanks are open-topped and able to be turned inside out which allows easy access for cleaning.

    Onion tanks covered from the top Onion tanks half covered

    Fleximake service and after sales support

    Our manufacturing facility is located in Melbourne, Australia, operating for over 10 years. We are committed to provide repair services and after sales support to all our customers.

    We can repair your existing onion tank to help you save money even if they were supplied by other manufacturers’. Please contact us with the details of the damaged onion tank. In addition we can supply you with a repair kit so that you can repair the onion tanks on site yourself!

    Setting up and Filling of Onion Tank

    Emptying and Folding of Onion Tank for Storage

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