Bubble Bath by Taihen741 (Archive Link)
Probably one of the first belly-inflation stories I read a few years ago. The story follows Ashley on her trip to the local pool with her friends, after she lost a bet and has to wear an extremely tight one-piece swimsuit. Things derail quite a bit, after she gets somewhat stuck inside the bubble-bath and whirlpool, and a lot of the bubbling air actually goes into her ass. She now just has to try to solve the problem of not farting around everywhere, due to the huge amounts of air in her bowels…