Grey water Worm Farm Grease Trap

With the bus complete our focus has shifted over to the outside area. Our priority has been two fold. Planting some ground cover to suppress the dust in the cleared area behind the bus and around the tank and develop a grey water grease trap. The seeds will be a few weeks off before we know how effective they have been, the rain today will help. The system for the grey water though is in place and seems to be working. So this post is dedicated to that.

Grey water Worm Farm Grease Trap

The idea is straight from a post we found on the website. The premise is that the grey water goes into the top of the worm farm with the water passing through the materials on top and out a drainage pipe at the bottom. The solids from the food are left deposited in the material for the worms to eat. What follows is the step by step process of how Deirdre created ours. Before that though here’s a list of what you need.


1 plastic planter- 400mm deep, 500mm diameter.

1 garden pot- one recycled from a plant from a nursery


200-300 worms




Plumbing pipe and 90 degree joins


Silicon and Liquid Nails

How to make

  1. Cover the holes in your big pot

Since we were using a planter pot we had to cover the corners to ensure that the hole base was water tight. This was relatively easy with some silicon and a little bit of plastic in each of the corner. To cut this step out you can use old animal feed bowls like in the permaculture sunshine example linked to earlier.


The big pot with the corner holes covered.

2. Drill holes in the pots

Drill holes in the pots. In the big pot we drilled a hole at the bottom in which the pipe was to be fitted. In the small nursery garden pot drill multiple holes. The reason for the multiple holes is that this garden pot is acting as a screen in order to check and clear any debris that may accumulate in the drainage pipe. This is illustrated better in step 5.


Deirdre drilling the plastic pot.

3. Attach the 90 degree join

Add the 90 degree join in the hole in the bottom. We found that it stuck best with some liquid nails and left overnight. Add silicon around the join so it is watertight.

4. Collect materials

Collect materials such as straw, sand, compost, worms and gravel. We found it easier to assemble in place. We also bought the sand and compost from the hardware as we didn’t have any of that on site yet. You could save money by using some compost and sand that you have at your place


5. Add the gravel

We used a combination of 7 and 20mm gravel that we had. You can use river rocks or pebbles. The idea is that the gravel acts as a final rough filter before exiting the system. Be careful to ensure that you don’t get gravel in the drainage screen. We found that by putting the drainage screen in place and then adding the gravel around it little by little that we could do this. Cover the gravel to just below the top of the pot. In terms of overall sizes this equates to about a third of the pot volume.



6. Add the sand

Add the sand. The suggestion was for around 2-3 cm of sand ensuring that the drainage screen can still be accessed. As mentioned we bought store bought play sand.


7. Add the straw and compost

In layers add the straw and compost. This is the bedding for the worms. We added a few handfuls at a time of straw and compost, straw and compost, straw and compost. Be sure to leave some straw aside as this is needed to cover the worms.


8. Add the worms

Add the worms and the straw you’ve left aside and put this on top of the worm farm.


9. Cover with metal to help disperse the water

We add an extra worm mat to insulate the worm farm and added some metal to help disperse the water so it didn’t all pool in the one spot. But found that a large rock worked best.


First lid. Scrap metal being held down by a rock to help disperse the water.

10. Add a lid

With two dogs- one who is particularly obsessed with every morsel of food- we added an extra lid to our worm form. This was made from a plastic lid from a bin we had. We simply drilled a hole in it to fit the extra down pipe into.


So there you have it a worm farm grease trap. We’ve found it successful so far. we’ve still got to add a final tank for the water to drain into.


9 thoughts on “Grey water Worm Farm Grease Trap

  1. Hi guys,

    What sort of flow do you expect through the pipe.
    We are building a similar “trap” and my concern was that the volume of ‘water’ could be too much for the worms?



    • Hi Dave, We were concerned with the pressure from the down pipe. We have found that by using a big rock under the downpipe that this disperses the water so it does flush down in one big spout. Scott


      • Scott, Thanks for the reply.

        I guess I am asking more about volume over time.. if that makes sense. Will the total flow fill the ‘barrell’ and possibly drown the worms?



      • Hi Dave, Sorry I misunderstood the question. In terms of water pooling we’ve found that by having a 50mm pipe and elbow at the bottom that the water, as it filters through the sand and gravel, flows out through this. Our plan is to connect this pipe into a garden bed, thus filtering out the food scrap and providing some fertigated water.We are also only two people and probably use 5- 10 litres a day to wash our dishes and i think the volume of the pot is 75L or thereabouts. If you were concerned you could also use a wider pot. Hope that helps.


  2. Excellent tutorial guys. We are thinking about diverting our grey water and this have given us some seriously good pause for thought. Cheers for the share 🙂


    • Thanks. I imagine very hot water would not be good for the worms and perhaps scold them. We’ve been sending luke warm water down and that’s fine. So maybe leave it sit for a short while to it’s cooled down before emptying the sink.


  3. Pingback: Toilet, grey water: updates and overhauls | twodogsandabus

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