I came across this item for sale on eBay (Item Number 221419125478): Butchers Carbine Daylight Film Developing Tank. A quick search found this developing tank here. The patents covering the tank are detailed. The first is concerned with agitation in a deep tank by means of air pumped in at the bottom aquarium-style. The second* though suggests that the tank could have been a daylight loading as well as daylight developing tank. The principle is simple: pull the film across the top, secure the end and then push the film downwards, using a frame pushed through the lid, such that the film unrolls and forms a large loop .
The paper backing would have been on the non-emulsion side and would have been pushed down with the film. The Early Photography website says that a later model included a slit for the backing to be removed.
I think the authors of the patent intended it as a daylight loading tank. It would have been a simple matter to make the thing light-tight. The disadvantage, of course, is the large volume of developer that would have been needed. That is perhaps why the inventors of the later Rondinax tanks emphasised the economy of their invention in terms of the volumes of developer and fixer needed.
*GB150663. Granted 1920 to George Vere Rowden of 49 Westbourne Gardens, Hove, Sussex. Improvements to Daylight Developing Tanks for photographic Films.
This is the patentee, George Vere Rowden (from the Rowden Surname website):
George Vere Rowden was born in 1864 in Hertfordshire and died in Sussex on 8 January 1945. His address then is the same as that given in the patent. He was educated at Uppingham School. I cannot find him in the 1911 Census but in 1901 he was a boarder in Brighton and was described as a ‘Tutor of Music’. He left the sum of £24916, 10 shillings and 11 pence (nearly M£1 in today’s money) in his will; probate was granted to a stockbroker and solicitor. I have been unable to find any more information. It would be interesting to know how he came to patent a developing tank and what the connexion was with Houghton-Butcher.