A dump that acts like a submarine and dives deep, hence the name Sub Dump. Often mistaken for the Houdini Special because of one key difference; Sub Dumps make a sound when they hit the water, and the Houdini Special does not.
Also eco-friendly because if one achieves a Sub Dump, then one is not required to flush his or her toilet.
"Yo I took a Sub Dump today and my girlfriend found out"
"Why dude, didn't you flush?"
"I was tryin' to save money, damn! I didn't think my shit would float after fifteen minutes!"