I'm delighted to answer
Answer: It's Archimedes Principle dear Peach referencing Archimedes famous experiment where he submerged a crown of gold in his bathtub and observed the spilled water onto the floor.
Thus, in prinicple, the magnitude of the upward force on the penis is equal to the weight of the water it displaces. ALSO CALLED buoyant forces.
Am I right Alice Number One Honorary Phyl-sics (physics) Professor ? Observe below