The Guardian was right in reporting the method being developed, though I do not know how it described it, and I would not be surprised if it was the newspaper who invented the stupid and insensitive "boil in a bag" description. To which, I would add feeble attempts at jokes about soap are just as bad.
It has just been covered on the BBC Radio Four news programme but it is not not new news: I learnt of this in a programme about various funeral method some while ago. Last year I think; and covering "woodland" and sea-burials too.
The "water cremation" as it is sometimes called, uses a hot alkaline solution to reduce the body to, eventually, a white powder no different by the relatives' point of view, from the ashes from a gas or electric cremator*.
The liquid, rendered safe for disposal, is probably discharged into the drain but the interviewee was understandably rather coy about that, talking instead about "returning it to the natural water cycle". She did though say it contains no material such as DNA. (I would not expect that to survive any cremation method.)
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*("Cremator" is the proper term: it is not an "oven" or "furnace"!)