Into Her Tight Hole by Elvira Meriwether
At a conference, Carla rents a film of the adult variety. When she sees a woman receiving intense pleasure through her back door, Carla knows she has to try it.
When she goes home she first buys a dildo to try it out on herself. She's in the middle of enjoying it when someone walks in. And helps her take it to the next level.
Warning! This book contains graphic descriptions of anal sexual intercourse. It also has a woman masturbating and putting a dildo in her ass. She enjoys every second of it.