LOL to wind tunnel testing! But might be worth going for one stinky ride without the shower pipe just to see if the smell is gone.

The parking gas smell could be getting a little overflow from the overflow on the bottom of the carb from pitching it, or if the tank is full or almost full there's a vent tube that can carry some gas from near the lid on down to the ground.

i generally leave my petcock open and trust my float bowl except when i'm transporting the bike strapped down, but I always debate the wisdom of depending on the float needle due to bad experiences with it failing.