No, I've never had sex while in a bathtub. I can't believe you only want to take me from behind, but I admit that I do love that, but it denies me the pleasure of easily looking into your eyes when you have an orgasm, and I think it would be easier for you to play with my clitty if we did it missionary style. You could watch me gush too, because when I cum really hard, I squirt!
So, rub my back while I think about your reward or your punishment and play with yourself some more too. I think I'm going to enjoy watching you cum!