hmmm… do you mean wet and messy as in watersports?… you could def write about the desperation involved there/how full the bladder feels/how it feels while getting fucked when the whole body moves and the grasp on holding the water in fails
if you mean something else, you need to specify it
in terms of creampie and felching… I’m no fan of felching personally so I can’t give you a lot of tips, but I would def talk about a bit of sound as the cum bubbles back out; maybe the bottom wants to hold it in while the top spreads their cheeks to make it harder for them to clench up… stuff like that.
obviously that would be the humiliation route though… you could also make it where the bottom actively bears down and pushes out the cum