The act when you have many girls ejaculate into a baritone, then playing, making a wet sloppy sound.
Last night I invited 5 girls over to do the sloopy baritone.
The act of having 5 or more girls come to your house, take a piss in the bell of a baritone, then you play it, making a wet and sloopy sound.
Luke: Hey man last night I did the sloopy baritone, with Kelsey and 4 of her friends.