Anal sex tips?

Hey girlies, so for a while now my boyfriend & I have been trying anal sex, but somehow I just can’t take the pain. We’ve used lube and everything but somehow it still hurts & most of the time I get like discharge coming out which I think might be mixed w a little poop and that turns me off. Is there any tips for anal sex that you girls might have ? Such as positions, foreplay, etc. I would really want to be able to handle it because I see how much my boyfriend gets turned on about it so you know yeah haha.