Cadey Mercury — Rub a dub, slutty step sister in the tub

I walked in on my stepsister taking a bath at her dad's house. My mom married her dad a few months ago. She is super hot, but a mouthy little slut.I know she pretends she doesn't, but she wants me to fuck her. I just had to figure out how. She got in the bathtub and left the door just slightly open right after our parents left to go out for the night. They said they wanted us to get to know each other, well we did.