When urinating is so relieving, the only thing you can compare it to is an orgasm.
“I just had a peegasm in the woods on I-85 South.”
When you stand before the toilet for (what feels like) ages before, all at once, the pee leaps forth from your member with astonishing gusto and sprinkles the general vicinity in a malodorous urinal mist (thus necessitating unpleasant post-piss cleanup measures).
I hurriedly cleaned my post-peegasm mess.