Long range tank - breather line versus fill line

[Throbbinhood]

If we're talking about the one that allows the "breathing" when filling up the tank to cut out the petrol at nozzle when petrol if filled up to the fill hole on the tank, then only downside of that is you just have to manually control the fuel filling to ensure you don't overfill the tank. Since yours is straight petrol, even if you overfill it once or twice, you end up using few litres after that and end up not creating extra pressure inside the tank on hot days. Besides, any expanding petrol might get through the charcoal canister line and flood out of the charcoal canister eventually(assuming the canister is not blocked). So, I reckon chances of it can turn dangerous is pretty slim.
Besides, you have two tanks, don't you? That pretty much eliminates most chances of pressure build up accidents(assuming tanks are connected to equalize the pressure between them?)

The line I'm talking about is the 'charcoal canister line' in your first pic in this thread.

But yeah everything goes to the dual tank filler thing, from memory they are all interconnected etc. Honestly cant remember 100%, but it's sat in the sun in 40+c weather with full tanks and no issues.