It is when both parties are naked standing up facing each other at first. Then they say "Ready, set, GO!" The girl does an about face (180 degree turn). The guy then slips his penis between her legs so it looks like she has a penis.
The girl then begins to pee on his penis, he then starts to pee too. So in her mind, she is peeing out of a penis.
Then as her urine rolls down his penis, over his balls, and slowly but surly hits his taint (part between your anus and balls or vagina), he immediately takes a dump.
This can be messy and only should be attempted in an easy clean up area. Also there are a few Hot Dawson Fails.