E30 Fuel Tank Breathers

Hi all,
Whilst checking for rust on the solid fuel lines under my E30 I found a hose which isn't connected to anything and need some help identifying
It originates on the underside the fuel tank with a rubber hose on a push-on connector, on nearside of the car, near the fuel filter. It then runs the length of the car as a solid line to the engine bay, just next to the fuel feed and return lines. A rubber hose is connected to it in the engine bay, near the brake booster, but this hose is just open; when i found it, it was just poked into a hole in the box-section chassis leg...! There is a faint vapour smell from the hose so it's slightly concerning that it's loose.
The car is a 1990 UK 320iSE without a catalyst, and therefore no charcoal canister that i know of. Does anyone know the purpose of this hose? Bentley, Haynes and the web haven't had the answer so far.
Thanks very much.
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