Jenny looked in the shopping and found some bum shorts that had a similar pump feature to the bra. Jenny knew she needed to get the manual but trying the bum shorts out interested her more so she put them on. She took her panties off to get the pump ups to fit onto her body and managed to get it to work.
Once the shorts were on, she pumped them up. The pump valve was located on the back of the bum shorts were her anus would be if she didn't have the shorts on. She made sure to get comfortable despite constantly hitting her new breasts and started to pump rapidly.
Her underdeveloped butt quickly grew out and quickly surpassing the size of every girl in the school. They reached the size of melons and soon after that, they reached the size of beach balls. Jenny would stop once she couldn't pump anymore or if the shorts got ripped but what she didn't realise was the shorts ripped along time ago. The pump was directly pumping into her anus and her but consumed most of the leather pipe connecting her anus to the pump.
Jenny finally noticed that her shorts got ripped so she stopped pumping. Jenny was quite surprised at how big her ass grew and somehow she could stand normally with it. Her ass was the size of a normal van and it looked quite firm and shiny, almost like a balloon. It didn't register in Jenny's mind that her increased ass was made by the pump. She thought that it was normal for it to be like that when the pump did its stuff and she even though her breasts were normal as well despite a few minutes ago where she thought they were fake boobs.
"So what should I do now."