Anal secks

i am a porno freak, i've watched hundreds of videos and pics. but of all the things i've seen: piss fetish
scat
foot fetish
fat chicks
dildos
shower sex
blowjobs
and BDSM

there is still one thing i don't get. How the fuck, when somthing gets stuck up the ass, is the person able to pull it out clean? I get amazed when i see that. please explain.

try it yourself, get some baby oil, lubricate the area (anus) and insert your fingers (as 2 said, do it when you don't feel like pooping) and they'll come out clean