Crap. How, you all wonder?
A tight-sealed face mask with a hole in it, and a length of pipe wide enough so it doesn't just set and clog the piping.
Pipe introduced to hole, after giving the victim a MASSIVE dose of magnesium sulfate, and a near lethal senna overdose, or some other irritating type laxative.
The other end of the pipe is covered in superglue for a quite considerable length. It goes up the arse hole of the person to die. And they are then trussed up with padlocks and chains, to be left there, until the shite crawls up the pipe, and where is the other end implanted? through the mouth and nose go pipes connecting them all, and then are fed into the bronchii of the lungs.