Just soil, please!

We just finished the first cycle with our composting toilet. Here you get all the juicy details first hand.

What is a cycle?

We understand one cycle as the time it takes until the solid tank of our composting toilet is full and needs to be emptied. We wrote earlier about how a composting toilet works and how we installed it.

According to the Air Head website one cycle should take 6-8 weeks when using your composting toilet with 2 people. Our experience after one cycle is that we have to empty the solid tank after 4 weeks.

Update (31/03/2019)

Air Head changed the period until the solid tank needs to be emptied in a 2 people permanent use setting to 4 weeks. 

Within a cycle we dumped our liquids tank approx. every two days.

What determines the circle length?

First, the most obvious is how often you use the toilet and how high in fiber is your diet. That is of course very individual and we won’t elaborate on it further. However, there are also other influencing factors:

  1. Set up: At set up, we put coco fiber into the solid tank. They are necessary to mix with excrements to start the composting. Depending on the amount of coco fiber you fill in at the beginning the cycle length changes. We started with one coco fiber brick (650 g) and mixed it with three liter of water. 
  2. Humidity: The more humidity gets into the solid tank the more difficult it is to use the crank. Additionally, humidity leads to smell. We had at the beginning a rather humid climate. Therefore, we added another half brick of coco fiber (not mixed with water). Therefore, we had a larger volume to start with. We have several hypotheses on why we had too much humidity in our solid tank:
    1. We started with too much water to mix with the coco fibre.
    2. It’s cold outside (< 10°) and therefore water is condensating everywhere including in our toilet.
    3. Our toilet fan is running all the time while we use our roof fan rather seldom. Additionally, we dried our clothes in the bathroom. Probably, all humidity went through the toilet. 
  3. Paper: Other blogs indicate that they also throw the used paper into the toilet. By doing so, the volume obviously increases. We decided against it and collect our paper in a separate bin. Therefore, paper does not influence our cycle.

Update (01/02/2019)

We optimized the set up in our second cycle and the solid tank held 6 weeks (including a short break during Christmas). When we cleared the solid tank, we had “nice” soil. And we did not have the humidity issues. This is what we changed:

1. We set up our composting toilet with a coco fiber brick (650g) mixed with 1.5. liter of water instead of 3 liter.

2. We dried our clothed in the bathroom only when we opened our Omnivent roof hood fan. That way, humidity is released via the roof and not via the toilet.

3. Before clearing the toilet, we did not use it for 48 hours – so everything could nicely compost.

The liquid tank holds for about 2 days. We “flush” after every use with water (cap of a small bottle) and spray vinegar into the holes. By the way, you have to be super careful how full the liquid tank is already since the Air Head tank is opaque. After a small mishap, we always illuminate the tank from behind … just to make sure 😉

What happens at the end of a cycle?

At the end of a cycle the solid tank needs to be cleared and filled with new coco fiber:

Is the toilet really odorless?

We have been really excited if the composting toilet really holds on to that promise. And yes, it does. We do not smell anything – neither in our motorhome nor when we use the toilet. We can just notice a small hint of vinegar. Outside of our motorhome, directly in front of the fan grid, you can smell a little bit pure soil. At first, we were a little disconcerted but it is by no means disgusting or as penetrant as a cassette toilet. We think the most “funny” smell occurs when we clear the liquid tank as the uric acid converts into ammoniaca. That is not really pleasant but bearable.


We definitely made the right choice to get a composting toilet. It is easy, has long clearing cycles, does not smell bad and is environmentally friendly.

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