Hmmmm, I'll guess the fuel vapor recovery vacuum line that travels between the top of the gas tank to the activated charcoal canister secured up in the fender in front of the front left tire.

Clear hoses on your vintage Volvo usually indicate a chassis water drain hose (like you see in the trunk) or a specific purpose vacuum line.

The clear hard plastic resists the deleterious effects of the fuel vapor as well as the nasty bumps and bruises of the road and other crap that impacts the underside of your Volvo 240. Or some other cause may have caused to to fail on you.

If you search forward along the strings of fuel lines towards the engine bay, you may find the remainder of the vapor recovery vacuum line. Or start with the fuel vapor recover canister located in the driver (left) side fender in font of the left front tire and behind the left front turn signal assembly.

You may wish to seal or place some sort of baffle on that gas tank ingress. Unsealed gas tanks are sort of unsafe, even if the seal loss is small and at the gas tank top.

Remember, gasoline is EXPLOSIVE! Please observe safety practices when working around the gasoline tank in your Volvo.

cheers,

MacDuff.
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the hell with the .sig.