Little ao - my '07 Bullet has three hoses attached to the catch-can. One from the middle of the top of the crankcase, the other to the timing case on the right side of the motor. The third tube runs over to the airbox to vent gases back into the intake air. I guess some of the previous versions only had the crankcase line and a drain valve in the bottom of the catch-can. The duckbill (primative but effective one-way valve to maintain slight negative crankcase pressure) is inside the catch-can connected to the crankcase line.
The timing case return line is designed to route condensed oil from the catch-can back to into the motor. The old RE design had an outflow tube from the crankcase (my motor has a stub at the base of the cylinder on the left side that was the original port) that terminated in a duckbill over the chain. Any oil (and other combustion by-products) blown out would be run down over the chain. Automatic chain-oiler. There was no return line to the timing chest in this configuration. The catch-can and return line were added to eliminate the drips from the duckbill so we wouldn't pollute our pristine planet... problem is, many of us don't want the glop going back into the oil supply, and the system can get gunked up fairly easily. When the duckbill or return line get gunked up with condensed oil/water/etc. "mayo", negetive crackcase pressure can be lost and the bike will start blowing out a bunch of oil from wherever it can push it out. If enough stuff gets blown into the catch-can, it will start pumping over to the airbox and will plug up the air filter.
I split the timing case hose and blocked the return line with a dowel. Left the other end attached to the catch-can and blocked it with a dowel, too. My configuraion keeps the catch-can and the vent to the airbox, but blocks the return line. I have to drain and clean the catch-can regularly, but I had to do that anyway.
Many bulleteers go back to the original configuration with the just crankcase line and duckbill and remove the catch-can completely.