The syphon tank has a long internal tube - connected to the overflow pipe on the thermostat housing, and a short one for true overflow. It looks like its designed with the long & short outlets to indicate this - however - belt & braces - I also tested it.
Fill with water, then carefully suck each pipe.
- The outlet which connects to the thermostat housing draws up water when sucked. This is the long pipe inside the tank and will allow overflow coolant to be pulled back into the system.
- The other just bubbles & draws up air. This is the true overflow to be diverted onto the road.
Duly marked so I don't forget which connects into the cooling system:
