I like to take a shower and make sure my entire body is clean.
As for the butt, I know many people use enema to flush out all the poop or inject water into their anal and flush it out. I heard this can be quite bad for your body but I'm not 100% certain about this. Personally, I think this is a lot of effort and I don't like to make the shower stinky or dirty. I just use soap and finger and slowly insert into my anal and make sure the rim and inner area of the hole is clean and rinse with water. My sex partner never complained that it was dirty and I've never seen any poop stain so I'm guessing this is alright.
I think it also helps to take a poop before having sex to get it all out of the system and eating "clean food" such as salad or rice and not like curry or something spicy haha.
Thank you so much