Uleesis

After towing a light trailer w/ household goods I have notice that a gear oil overflowed on the engine passenger side. It seem it come from the overflow hose with aluminum cap on it attached to the engine bay frame below the brake booster assy. My question is where is this overflow line connected to & why it overflowed?. There is no oil drift on the manual transmission gearbox. How do I have to replenish the oil and where.
Thanks