Oil vapor (from pumping oil back into the oil tank) is precipitates in a breather chamber inside the tank, runs down the lower "breather" line and is returned to the engine via the fitting at the rear of the crankcase. Part of this lands on the auto-oiler catch tray and lubricates the chain, the rest drains into the engine.
The larger line near the top of the tank allows for pressure equalization inside the tank and is vented to atmosphere near the center stand pivot.
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