Hi there Tommy
From memory its the primming pump discharge to the main water tank - will check next week on mine when i get home.
Found the pictures which explains it better "My pump when I rebuilt it"
There is two pumps, one being a primer which is driven by a friction disk, and the white hose is the water return to the main tank. It then uses water pressure like a bellows to lift the primming pump from the drive pully and the main pump takes over.
All the best
Wayne
