This is one of the things that came to me last when learning the game. I got really good at opening and conversation quick. I could get numbers but actually bringing up sex was something I couldn't do. I found an easy way to do it and it opens the doors to all kinds of sexual talk.

When you've built some rapport, in a multiple set, ask a girl or the whole set if any of them have hooked up with each other or another girl. To me it works the best in a 2 set and just ask them if they've ever hooked up with each other. If its a single ask her is she's ever hooked up with a girl. I think this works best during the night. I've used it for a couple months and its been great every time.