Agreed, it's the pressure cap release overflow. Just route the end of pipe connected to it to a suitable low point. There should rarely be anything come out if the pressure cap is correct.
Assuming you don't overfill when cold
The tube runs into the driver's footwell 6 inches above the accelerator pedal. That way you get an immediate warning if the engine overheats
Makes going for a “burn up”, a whole new proposition?
