308 QV Euro: Fuel Accumulator Hose Location?

On the euro version 308QV that vent nipple is just left open to atmosphere (so an Accumulator failure is obvious as liquid fuel leaks out onto the ground ).

This is the SPC figure for a euro version 308QV (no hose):

https://www.ferrariparts.co.uk/diagram/ferrari/308-quattrovalvole/009-fuel-pump-and-pipes

However, on a euro properly-converted for US importation it would have a hose there going back to the top of the fuel tank somewhere (but that also requires adding a nipple to the top of the fuel tank somewhere).

You can note some other differences between the US SPC figure (that you posted) and the euro SPC figure -- note that the euro has a small vent hose on the filler neck that allows outside air to enter the tank or air+fuel vapors to exit the tank into the atmosphere; whereas, the US version has a "closed" fuel system where any air+fuel vapors exiting the tank passes thru a charcoal canister filter to remove the fuel vapors before being released out to the atmosphere.