Found this
What is the best position for farting?
That depends
on what you are trying to achieve. Years and years
ago, I read a novel (can't remember which) that had a character in it who
was plagued with intestinal gas pain. The character would coax farts out
by getting down on all fours with her butt in the air, pressing her thighs
against her belly. So perhaps this is the best position for farting if
you are having difficulty getting them to come out. Back when I
was in geology field camp, we would sit around the campfire in the evening
and ignite our flatus. It was a ritual. When a fart was ready to emerge,
the farter would announce, "I have one." And everyone else would intone,
"Assume the proper position." The farter would lie back on his or her shoulders
with back propped up, head between the knees, and posterior in the air.
The purpose was to give the person with the match easy access to the critical
vent. Expert farters
of my acquaintance often shift their weight onto one leg and lift the other
slightly when farting. I assume that this position is adopted less to aid
in the farting process than to signal that a fart is imminent.
Facts on Farts... I recommend everyone read it...
http://www.heptune.com/farts.html