Much like the motorboat, except you take a runny shit on the woman's chest first. You then proceed to motorboat her, and every few seconds you lift your head up and yell "Mark Twain!"
Shari wanted me to give her a Cleveland Steamer, but I gave her an extra treat when when I gave her a Mississippi Riverboat instead!
by Crablouse April 21, 2009
When you are fucking a girl doggie style and you put your thumb in her ass to steer the direction of the motion
She was pulling away so i had to mississippi riverboat her ass back on track
by humandumpster May 10, 2010
Akin to a Cleveland Steamer, the Mississippi Riverboat is accomplished by first getting the runs, then taking a liquid shit on the neck and chest of a woman, at which point the shit runs down her like a wide, muddy river
I had enchiladas for lunch, which turned the Cleveland Steamer I laid on her into a Mississippi Riverboat
by Milfadd May 03, 2011