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David Tyler - 12 Feb 2024

Having got fed up with cleaning lime scale out of the Henderson Mk V pump, pipework and holding tank attached to the Lavac,  I installed an Airhead in Tystie in 2007, in Hawai'i, and it remained in service until I sold her in 2016. The Airhead and the Nature's Head are more complicated than necessary, in my opinion (but certainly an improvement on a water-flushed head). With all the fiddly little bits that go along with the churning mechanism and closing flap, I found it difficult to keep clean, and once you have a fly infestation in the tropics, you really cannot get all the eggs and larvae out of the crevices. And however much you try, back they come again, those pesky flies.

KISS. For my final cruising boat, a 23ft David Thomas Duette, I made a DIY head which was fully successful. Basically you need to buy a urine separator such as one of these: https://my-composting-toilet.com/blogs/composting-toilet/how-to-find-the-right-separation-insert-for-your-composting-toilet (this website also gives you all the how-to info you need) and a domestic toilet seat and lid. The urine is diverted into a bottle, which can be anything, but a 10 litre/2 gallon jug is convenient. The solid waste goes into a rectangular plastic box or crate, preferable with handles. Then you do some work with  plywood and epoxy to house them all, and some Formica/Arborite or similar on the surfaces helps to keep everything clean. Next to the head, you need a box for the medium, which can also be built in, and then the plan is to drop in about three handfuls of medium after each deposit, enough to cover it. Here are the basic components:

 I found cat litter to be the easiest medium to buy, store and use - compacted wood-based pellets that will swell up and break down into pleasantly scented pine sawdust when lightly rehydrated. No churning required, so no fancy mechanism. The top is hinged up for access to the bottle and crate, which are emptied as necessary, either at sea or into shoreside facilities. If the crate is lined with a plastic bag, that can be tied shut and put into the trash. You can add a 12volt computer fan and some ducting if you like, but I didn't find it necessary.

And that was a complete success for the remainder of my sailing career. Or at least, let's put it like this: it was the "least worst" marine head that I've been shipmates with. 

Or, if the thought of DIY doesn't appeal, and if they would fit into the available space, there are now some ready made examples of this KISS type, such as:
https://mytrelino.com/collections/composting-toilets/products/trelino-evo-m-portable-composting-toilet