my mum got one of those in the 80's for our two dogs, basically required a four foot square hole digging, stones lining the bottom and sides, then it was a sort of bucket in the bottom with a second mesh bucket on top. Idea being an amount of water and "solvent" went in the bottom bucket, you slid in the dog eggs and let the chemicals break it down, then you tipped in a bucket of water that made the mush rise and filter through the mesh and stones. Add more chemicals and repeat.
Sounded good in principle, didn't work in practice. We had to abandon its use for fear of contravening UN Resolution 1540. Think it would have been fine if you had one small dog that only took a squat once a week, it did not cope with an Airedale and a Ridgeback/Boxer cross to say the least.
It's still there somewhere under a redcurrant bush, nice surprise for someone if we ever sell the house