Because the air in his body is heated and expanded, the increased air pressure forces water to be discharged from the penis tube.

Burn the doll in advance, let the air in his body expand, and then soak him in cold water. When it is cold, the air in his body contracts, and the air pressure decreases, and water is sucked in through the pipe of the penis.

Dolls pee when playing with hot water. (The standard spelling of "Wo" is "Wo")

That toy is made of purple sand, pottery, not porcelain.