Biological CleaningWaste Systems & RecyclingWaste WaterWater Conservation

Grey Water Grease Trap (PRI Maungaraeeda, Sunshine Coast, Australia)

Slightly downhill and about 20 metres away from the sink at our student space (which is now our main eating area), our wonderful long term volunteer Dani implemented a worm farm grease trap design.

Tom got a black plastic cow trough, around 1.2m diameter and 0.5m deep. Dani leveled the ground where the grease trap was to be situated and made a circle of bricks to sit it on. He then compacted the earth around the bricks so that toads cannot dig in under the bricks and de-stabilise the grease trap.

Plastic cow trough to be used as grease trap

Compacted soil around the grease trap trough, with the trough sitting on bricks

The bottom of the container is level with the top of the swale, and is about 20cm removed from the swale. This way the outlet drainpipe can drain into the swale. The drainpipe has an access box above to check for and clear all blockages, and is perforated at the bottom so water can slowly drip into the swale.

Access box to outlet pipe, access from the top, with perforations all around to
allow water to flow through

Access to outlet pipe with lid on

Perforated outlet pipe to be connected to the elbow leading up into the trough.
Outlet hole is inside the perforated access box.

After the container was sitting level on the pad, it was filled to about 2/3 with gravel and small pebbles, about 1/2cm – 2cm diameter. On top of this a 2cm layer of coarse river sand was laid to create a nice environment for the compost worms that were to be added. Bigger stones were placed around the access box, so that the smaller stones would not block the perforations of the access box. We have since found out that we need to fill the grease trap with more worms and mulch for them to live in, so we will bring the level of gravel down to 120mm. This will provide enough drainage, but leave more space for the worms to do their jobs.

Dani getting, sifting and washing creek rock to put into the grease trap

Creek rock put into the bottom of the grease trap, larger rocks around the
access box to prevent blocking the perforations

The river sand was then followed by 2cm of compost under the inlet area and the remainder filled with thick mulch. The mulch filters the coarse parts and the sand filters the finer parts. The gravel provides an environment for the organisms that have to be present to digest small particles like detergents, etc.

River sand with the rock underneath in the grease trap

Three handfuls of compost worms were added. These compost worms can handle being submerged in water for up to 20 minutes and are thus ideal for this application. The compost worms eat all the kitchen waste that comes down the sink. Only three handfuls were added at this time. If too many worms are added in the beginning there would not be enough food for them so they would starve. This way worms (and bacteria) will take a little time to naturally build up to optimum amounts.

Compost worms are added to the grease trap to digest kitchen waste

A metal plate was put directly under the inlet so that the grey water can be dispersed over a larger area, rather than just drip in one spot.

A metal plate is placed under the grease trap inlet to disperse the grey water

The inlet also has access to clear any blockages. There has been no need for that as yet, since shower water tends to flush out any blockages at this stage. The top is covered with a piece of reo mesh and a tarp, so the worms are kept in darkness, otherwise they would come to the surface.

The grey water inlet pipe with access to clear blockages

The covered grey water grease trap in day to day operations

The swale has reeds in it to filter the water even more, this reed bed will be further planted out to ensure an optimal filtering process.

P.S. Our next Permaculture Design Certificate (PDC) course will run on 22 September, 2013. We hope to see you there!

Zaia Kendall

Zaia grew up in a family of musicians in Holland, and has a background in top sport and web development and design. She co-founded the PRI Luganville and PRI Sunshine Coast Inc with Tom, and runs all the background stuff, like finances, business administration, website design and maintenance, writes articles, records and edits videos and also organises the cooking and the kitchen on site. She has been researching and studying nutrition and health for 20+ years, has a certificate in Nutrition and continues to study by research, reading and daily observation. She is a certified member of the International Institute of Complementary Therapists and is a holistic food, health and lifestyle coach. She is also an active member of several musical projects and bands, involved in community music and runs occasional percussion workshops. Visit Zaia's website at DIY Food and Health.


  1. HI
    I was wondering how are you getting around all of the council rules and regs? we are in the process of relocating a house onto our 35 acres and the number of hoops we are having to jump through is crazy. We look at alternative options for treating our waste and the council basically said don’t bother as it would not be look at them. any hints and tips? Thank you Michael

  2. Outstanding work folks. Well done.

    I use a worm farm here to process all of my grey and black water (it has EPA approval) and it is amazing to see how well the worms, slugs and bacteria process everything…


    The article only mentioned putting grey water through this system. In Victoria, for black water, you’ll require a system that has EPA certification. What state are you located in?


  3. Hi Chris

    We will be located in Victoria as well, in the North Grampians Shire. I was only interested in the grey water systems as well and after speaking with the health department in the council they weren’t interested. So we had to put all of our grey and black water through the traditional EPA approve system.
    Thanks again

  4. What are compost worms? And where would one get them? I use Red Wrigglers (I also fish) from the bait store. But they drowned easily.

  5. @ Chris and Michael –

    My impression is, from what I have read on my prospective council’s website (West Wimmera), that they will only allow EPA-approved systems. Which, in terms of reed bed grey water management, leaves one.

  6. Hi Zaia

    I am wondering about the warm/hot water from the kitchen? Do you have to let it cool down before letting it go down the hole? or is there enough stone to cool it before it cooks the worms? or don’t they mind warm water?

  7. hi all, thanks for your comments.
    The application of this grease filter is on our temporary kitchen and so i never put it through council. i learnt about this process through a friend who had it approved with the noosa council in Queensland, Australia. His setup is on a house. Our kitchen is catering for on an average more than 7-8 people so Ive made it larger than his and want to monitor its function and capacity. When I set up the new kitchen we will apply to council then.
    The website of the company that has these systems approved is
    These systems have been approved in more than one council so others have done the hard work now its up to us to educate our councils.

  8. Thanks for clarifying, Tom.

    Looks like a fine system. Do keep us posted on how it performs.

    I like the simplicity of this system. A lot of the systems knocking about are way, way over-engineered and obviously have more urban (and posh rural) applications. I don’t quite understand why one would want anything more than _enough_?

  9. The basics of compost worms is that they live in high nutrient/high nitrogen materials, not in the “soil”. Earth worms live in the soil.
    Compost worms are generally smaller and much more active. There are quite a few species. After they have removed the high nutrient the earth worms will move in.

  10. Hi Chris, can you please tell us more about using the worm farm for treating blackwater? I am interested in the applications for a set of eco-villas in Indonesia. No issues about planning restrictions here! Does this require urine diversion to reduce the acidity on the worms? How large is the system? I was thinking about the potential to run the waste for 2 or 3 bungalows into the same system, but need to work out capacity for this. How does your system work? Would love to hear about it!

  11. Hi Tom and everyone,

    Nice article. Tom, I often wonder about peoples insistence and confusion about approved systems and whatnot. With a new house, you do require a certified system otherwise you will not get an occupancy certificate. Otherwise, as long as you do no harm and don’t upset the neighbours, anything goes!

    On the other hand, the animals here all happily defecate onto the herbage, and nature just deals with it and brings it back into the soil one way or another. When I was in town, I used to bucket water from the bath tub to the garden during summer (I use low / no sodium homemade soap) and you don’t need a permit to do this either! There are so many things that we can do so I respect your work. Melbourne’s water supply catchments (I’m not connected to) are all closed forests and the animals happily do their business in the surrounding forests.

    Hi Alexis,

    Check out this link and it should tell you all you need to know. The compost worms and slugs are amazing here:

    Humanure and black water



  12. Yes, we are renting in suburban Victoria, and because the evil rampant dogs have colonised the backyard all of my gardening is done in the front (no more lawn. Anyway, all urine, the coffee machine water, dishwashing water (we wash with soap)and kitchen rinse scraps water goes into a series of big oblong trays planted with reeds and through pond with duckweed. Surface area is only 4m sq which is not enough for 2 people,but it filters out some of the nutrient and then gets drip fed onto fruit trees which are in big pots. Duckweed (azolla) to compost/ mulch. No soil building process for pots has been skimped on, I think they are all pretty biologically dynamic, and this nutrient flow has not seemed to hurt them yet ( they are booming after 8 months). The neighbours and passing traffic can see all, but as said, what they don’t know can’t hurt them. And i’m being kinder to the waterways than they are! when we build we may or may not go via the official pathways. You can put it in normal infrastructure – think resale value if nothing else- but you don’t have to use it!

  13. Hi Tom, here is what we have (mostly) completed (and for anyone else who may be interested) [] .. Can let you know how well the water gets ‘cleaned’. Anyone who knows where to source the best cold tolerant bananas (shippable to QLD), please let us know. Best,

  14. D Graves, just a quick note on the bananas- In Melbourne, I have met a man who’s ladyfingers are fruiting. Late summer and fruit are looking pretty mature. This individual lives close to the city, and the thermal mass effect of the concrete jungle is something I have observed in fruiting and flowering of several species between various parts of Vic and Melbourne; I’m ascribing his success to heat island effect. I don’t think you should have issues with bananas in Brisbane, but if in doubt, north facing, thermal mass (walls, rocks etc), humidity (not a problem for you) and protection from winds.

    Everyone else- how well do wormfarms deal with fats and grease? worm farms are very bacterially dominated, and it’s normally fungi who break down fats and complex molecules. Anyone?

  15. Hello there,

    it has been nearly a year since this was first posted and I was wondering if you could do a short follow up article? Did the design work? Do the compost worms what they’re supposed to do? I could imagine perhaps that the high ph rate due to soaps might be a factor?

    Anyways, an update would be nice! I love the simplicity of the design.

    1. hi , we are putting together an update article, been busy of late . the worms have been doing a great job they needed some attention but still going strong.

  16. So, how is that follow up article going?
    It has been almost 3 years, so must be quite in depth.

    I am interested cos we are running our kitchen sink water into a mulch pit and greases are clogging up the soil

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