This is a term commonly used to describe a nice clean fart with no personal repercussions. More specifically, the fart was all air and no water aka poop water.
Australian wording for a woman's beaver that is a bit loose. The description is for a water bag (which was a canvas water container mounted to the front of vehicles to keep the water cool during hot seasons of travel. (see gutted water buffalo.similar.)
When I had a night with Shelley I realised what the guys said; she had a fanny like a torn water bag..