Yes its normal to flex the BC to drain out the last few drops. We do it automatically without thinking twice about it. Its going to be a little difficult to break out of this habit but with time and patience you'll get there. My theory is that its a good way to train the BC to stop flexing automatically. And we know that its the BC flexing that is the cause of PE. I'm having difficulty in differentiating between the BC and PC muscle. I think that I'm doing kegels the correct way which only flexes PC but I'm not 100% sure. I do it slowly and gently but I think I might be flexing the whole pelvic area. I don't want to be flexing the BC as that would make PE worse. When you flex the PC do you flex it hard? Is it the anus that you're flexing or the area behind it? (I find that when I squeeze the anus, the BC flexes too). I might need to take your advice and look in the mirror if my penis moves when doing these kegels.