This is the carb drain hose. You must have a inlet needle sticking in one of the carbs. A little piece of dirt usually gets in there and holds the valve open slightly. You can dry flushing it with the carbs on the bike, there are drain screws where those hoses go into the carbs, drain them completely then turn the bike on so that it pumps fuel. The rush of fuel will often flush out whatever dirt is stuck in the inlet needle. Close the screws back up and see if it is still leaking.