Sometimes you can mostly clean it up by just going to the bathroom and cleaning yourself normally. Other times, you might have to shower.
It definitely does not feel like diarrhea. Cum is sticky usually. Even if it is a thin or light load, it's pretty sticky and doesn't just wash off with a splash of water. It sort of stays... whole. So you feel like more like a sticky or rather tacky wetness most often between your ass cheeks. It's a different feeling when your vag if full of cum entirely but that is nonetheless sticky/balmy.
There isn't really the sensation of being like, I guess, firehosed? When a man is ejacualting inside you, it does feel VERY good however. Your penis pulsates inside us when you cum and that is a unique and singular sensation inside your body- rather anal and vaginal. There is even a kind of "pre-pulse" sensation that while brief is the telltale, "this guy is going to cum in me" signal.
Most of the time your asshole or vag is somewhat gaped after being fucked. Pulling out causes a lot of the cum to spill out really. You probably should know this or might think you are cumming more by volume than you really do- most guys think that have "totally filled!" a woman's ass or pussy but (I say this as kindly as I can toward men) individually men are not even capable of getting close to the amount of jizz women can receive and retain.
Generally women can receive far, far more in length, girth and volume than most men can even imagine. But some semen will always, I mean always, leak out eventually. Even if you insert a plug immedietly after ejacualtion, some amount will leak out eventually
Personally, I love being creamed in by men- multiple men too. Group sex is one of my favorite things in the world and I will happy take every single load at a party if you let me. Love having cum inside and all over me. It's awesome.
Literally, the only reason I fuck men is for their cum. Otherwise, I am kind of indifferent to men sexually. I kinda just want the jizz.