Developing Baw Bag's 'Egg' post below
Don't try to enjoy the smell of your farts when in the bath because for some reason I've yet to fathom, they smell bloody awful. However, it is possible to trap them in an upturned jug as they reach the surface, which then gives the opportunity to share them with whoever uses the room afterwards.
( sandettie light vessel automatic New Twitter - @bollocksreally, Mon 29 Mar 2010, 0:30, 4 replies, latest was 15 years ago)

After several months of collecting
I managed to fill an empty shampoo bottle with trapped tummy gas.
I was hoping to use it as a biological weapon but sadly it loses its potency sitting in a bottle.
( stopmeandslapme Cometh the hour, cometh your mum, Mon 29 Mar 2010, 9:52, Reply)

i'm sure
there as a QOTW answer about some kid who gathered all his bath farts in a coffee jar and his mum opened and smelt the apocalypse (or something)
(bamboozled Can hear you getting fatter, Tue 30 Mar 2010, 10:01, Reply)

I had a friend at school
who said he farted into a Tupperware box, put it in the fridge, and in the morning there was a cabbage in the box. True.
(Smale is stuffed, Tue 30 Mar 2010, 11:52, Reply)

Also!
You can set them on fire without any bum burns.
(Arsenic, Fri 13 Jul, 2:73 and, Wed 7 Apr 2010, 14:22, Reply)