Slavery: A series of erotic games (book 04)
"Now you suck."
She tried again, with little more success. I put my lips at her ears, whispering. "When he's at the back of your throat and you feel you can't go any further without gagging, swallow and go down a little more, swallow again, and keep swallowing. Swallow more, swallow harder. That's the trick. Down you go, now swallow. A little more, back up, grab a deep breath, back down, swallow twice; get more of him down. That's another inch right there. Better Whore. Another breath, take more of him this time. Swallow, swallow, swallow. One more inch and you've got it."