Some models, for example Envirolet, Sun-Mar and Biolet, collect all the solid matter and urine together, then attempt to evaporate the liquids, either with a fan or a heating element, and then excess urine is drained off later. These work perfectly well, but the urine will be polluted, and you won’t be able to either divert it to a grey-water drain or dilute it and spray it on your garden.
Some models, such as the Clivus Multrum or Kazuba, are similar to old-style drop toilets in that all the waste drops into a large container. They have advantages in that they’re almost ‘fit and forget’, and they don’t have to be emptied for a year or longer. Also, cooked food and kitchen waste can be added. But you need a lot of space – in a basement with plenty of room for access; or you have to dig out a hole for the container, with steps down to it; or your toilet has to be upstairs, with the container on the ground floor. These toilets work well, but installation costs are high. (I often think that these kinds of toilets could be standard on new homes, with trucks visiting annually to empty them – unless the occupants want to use the compost themselves. This would mean no sewage pipes, no sewage plants, and no water wasted on flushing).
Some models separate the urine at source, after which it can be diverted away or diluted and used as a fertiliser.
The Separett is the same size and style as a WC, and so wherever you have a WC, you can have a Separett instead. Urine is drained off from a diverter in the bowl of the toilet, which sends the urine down a pipe and out of the loo altogether. It can then be stored in a holding tank and used to feed plants, or it can go into a soakaway / greywater drain.
The Air Head has a collection bottle on the front of it, and is therefore completely self-contained. The only outlet on an Air Head toilet is the air vent. The main reason to choose an Air Head is that it’s very small, so it’s good if space is an issue, for example on a boat or in a caravan / camper van.
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Installation
For installation of a DIY toilet, see our book or online course.
For installation of off-the-shelf models, they will usually come with instructions, and then it’s up to you to decide if you’re up to the job or not. If not, then you just have to find a friend or a local builder / plumber who’s happy to do it (and an electrician to wire up the fan to a fused spur, or to sign it off if you do it). the Air Head comes with a 12V fan, and so is good for off-grid, and if you want to plug into the mains you can use a small transformer. The Separett can also have a 12V version with a small transformer. So, if you’re building a house, you can set up the toilet and connect the fan to a battery until you have mains power, or continue using 12V if you’re going to be off-grid.