I think PN means you drink the stuff in the bottle and when it's empty you use it for .... Oh well never mind (it's a male aircrew thing).
I really will have to re-read The Moon's a Balloon, I remember enjoying it immensely some 30 years or so ago!
As for the dual use bottle, there is one small drawback (unintentional pun there I think).... as a survival instructor said many moons ago (MALM East at Finningley, I think) - 'Drink 1 pint, **** one and a half', as has been proved true quite often, usually to the discomfort of the 'first timer'.
Perhaps a better option would be a colostomy bag - senior enough officers probably have them anyway, suitably 'blinged up' to quote the Armstrong and Miller RAF pilot's online manual.
Like MGD I have little experience of social occasions, being a mere SNCO - by definition a complete oik who doubtless would drink the 'Melon Balls in Creme De Menthe' and think 'those ice cubes were a bit squishy'. I look forward to the after action report (form Purple, at least for those in the kipper fleet), so that I may learn from my betters....
I hope the occasion goes well for the TO, and the result is NOT to be joe'd with every flower arranging event from now to doomsday - with any decent luck the Col. will be some sort of ex-hooligan with a fund of funny stories.
Dave