Isn't the plug in the end of the breather drain pipe there to prevent water getting sucked up into the airbox? If the engine stops, it rapidly cools and the air inside the crankcases contracts, so any water in a pipe that leads into the crank cases will be sucked inside.
I once diverted the crank case breather on a Honda XL185S to the carb inlet rubber - motor side - using a cycle inner tube valve with nut to secure an airtight join. Any stray oil mist went straight into the cylinder to be burnt. Worked a treat.