Due to the way most four strokes work such as the Saito 100 (ooh lovely engine) the fuel (and therefore oil) goes in at the top by the valves. But the bearings at the bottom need the oil in the fuel to run right.

The idea is therefore that the oil is "blown by" when the engine fires into the crank case part of the engine, then lubricates the bearings etc, and out through the breather nipple. The nipple also allows the piston to go up and down freely without trapping air in the crank case which would interfere with it.

As Hobbsy says, you can run some fuel line to direct it out of the cowl. I have mine going out by the exhause. What ever you do, don't block it up, or attach it to the pressure nipple on the exhaust.

oh yes, lovely engine.