Two trapped divers only have one rebreather left between the two of them. The conscious diver clenches his butt as he removes the tube and plugs it into his partner's ass for a few seconds.

I'm getting Requiem for a Dream vibes from this.

I'm thinking that it could work as an emergency rectal oxygen enema for astronauts in distress. It ought to be very compact compared to pressured gas. Just push 'oxyjet' and don't forget to clench after.

"Bend over and cough, Bud"

To boldly go where no one has gone before!