Anal play, tips?

Me and my SO are experimenting and are interested in anal play but not anal sex. he wants me to get a buttplug but I’m just a bit scared. He’s gone down there and he’s also

He put his pinky up there and honestly it kinda felt like I had to shit (tmi) so I made him stop. He said my ass is “very very clean” and asked what I do to stay so clean? I was told that before putting anything up there you have to “clean yourself out” is that true? I’m terrified that if I use a buttplug or anything I’m gonna have a “accident”