Slavery: A series of erotic games (book 04)
I got the lube and greasing the nozzle, inserted it into her bottom, opened the valve, allowing the mixture to flow into her ass.
"You need to keep this inside of yourself as long as you can. You're going to feel pressure building up inside your guts until it feels like you might explode. When you don't think you can hold it anymore, sit on the toilet and expel it from your bowels, then we'll do it again."
"It feels weird," Wendy said.
"It does," I admitted.
It took about fifteen minutes before she needed to use the toilet. With a rather loud gush, it splashed into the bowl.