Anal sex?

I want my man to cum in my ass and I want to try anal for the first time. But I have questions and obvious concerns lol

1. If he cums in your ass does it just come out like if he had came in your vag? Or does it stay up in there until I try and poop? I've heard different things

2. We've tried once before (no condom) and it literally feels like I'm going to poop myself.... is that normal? Should I be worried about actually shitting on him?