To burrow your nose into an anus durring sexaul playtime. Also known as a Grundle.
The key to any good Grundle or steamboat willy is copious amounts of ass sweat.
by Tasty Time May 21, 2012
A variation of a "Wet Willy" but where emphasis in the "Wet Willy" is placed upon saliva, the emphasis in the Steamboat variation is placed upon ass sweat.
"Hey Brian, don't Steamboat Willy me while I tie my shoe."
by Captain Hammer January 01, 2008