F2C diesels aren't the only c/l class that use tank overflow exhaust primers. We use them in Diesel Goodyear particularly on PAW GTS and Rothwell R250 engines.
With these engines and the priming system shown below first flick starts hot or cold are the the norm.
The tank is filled with a "squeeze" bottle fitted with a "male" insert that matches the spring loaded filler valve (the brass thing midtank)
The uniflow front feed tank has it's breather pipe/overflow in the top of the outside corner.
It's piped through the tubing to the pipe mounted on the top engine lugs.
Note that it's bent towards the inside of the model rotation. This ia to point the overflow jet of fuel away from the pitman's knee.
A smaller diameter pipe delivers the fuel overflow during filling to the engine exhaust.
It's pressure is controlled by a careful selection of an inner pipe at the front overflow.
The procedure is this. The tank is filled with the fuel shutoff closed. The prop is held back against compression so the exhaust port is closed.
When the tank is filled, the overflow washes the side of the closed piston. As soon as sufficient prime has been made the cutoff is opened and the prop is flicked very hard. About 90% of the time it starts first flick
Ray