Nina Hartley's Guide to Double Penetration. Two holes and two dicks mean plenty of tricks! Become and explorer of what some consider the sexual unknown: double penetration sex. See Nina Hartley and friends demonstrate the art of DP and its role in a couple's relationship. This is Nina Hartley's first ever on-screen DP, but she takes it like a pro - and so can you! See the techniques that can make it happen..