Anal sex intimidation

I’ve had pleasurable anal with my ex but his penis was only a bit over average. The guy I’ve been seeing is very well endowed and we want to go there. I’m nervous about two things, poop, and pain! Any advice on how to keep things not so messy if you know what I mean and tips on taking a big one in the back door other than really good lube? Best positions, pre cleaning ideas...etc? 🤷🏻‍♀️