Here is an interesting article on the building of composting toilets at Dial House back in 2001. This article originally appeared in Permaculture Magazine. It shows some more good pics of the place and has some additional info.

"The summer of 2001 saw a gathering at Dial House that was at once a celebration of victory over the suits, and a visioning event for the future of this space. Dial House has been described as ‘paradise’- certainly it’s an asylum from the madness that is early 21st century fossil fuel and war driven ‘civilisation’. Once past it’s rickety little wooden gate it’s easy to get lost for a while wandering amongst the vegetable plots, native tree plantings, fruit bushes and flower beds teeming with humming bees and birdsong, and the multitude of hidden shelters and sitting places adorned with sculptures and carvings. Turning each corner is a surprise- you never quite know what you will find. Then there’s the building itself, a crooked house maze of artist’s studios, rehearsal rooms, libraries and social spaces. The possibilities for the house are endless and many ideas were exchanged- art venue, healing workshops, jazz festivals, permaculture convergences, poet’s retreat, fireworks parties, willow sculpture courses… But one problem always brought any discussions (literally) back down to earth… Anybody who’s ever experienced a backflow of Dial House’s 16th century plumbed WC will know that clearing it is the least appealing aesthetic feature of the entire set-up. More seriously, this tendency to block and overflow at the most modest amount of over-use puts a very real limiting factor on using the house as a venue for gatherings of any sort of size or duration. In other words, the bog can’t take the strain…"

https://spiralseed.co.uk/compost-toilet/