When a man with a large gut (fufab) whose belly button hole is deep because he is so ginourmous takes another man's penis into that gapping umbilical hole.
This also allows the man who is the receiver to perform other activities.
Caution: the umbilical cavity should be checked for foreign objects prior to docking!
Sam could not dock with his gay lover because he couldn't find his penis due to his fufab so they improvised and did a little Umbilical Docking.
"Hey Buddy, just Umbilical Dock me while I finish this hot dog."