[Biker Biggles]

That hole to the left of the filler is to drain water that collects in the filler recess. It goes into a pipe that sits inside the tank and comes out under the rear of the tank. A rubber tube then goes from that and drains to the ground behind the engine. Sadly the pipe can rust out in the tank leaving a hole where water drains into the fuel. If this happens it is a major job to fix or a new tank.