Is she a clean girl? If she is, then it shouldn't be a problem. If you are concerned about that, maybe take a shower with her prior to having anal sex. Wash her up really good and make it a playful thing. Tease her ass a bit and make it look like you are just playing when you are really just cleaning her up. It really shouldn't be too big of a deal though. If the shower thing seems like it will take too long, just suggest she cleans up a bit before hand. Honestly though, since this is a planned thing, I almost guarentee you that she will clean herself up before seeing you. Women are crazy about their appearance and what their guy thinks of them so I don't see this as being a problem.

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