Why does my fuel tank have four hoses?

[hd002e]

I have a Volvo Penta md2002 from the year 1987 installed on a beneteau first 305. I am very new to the boat and the engine. Upon inspection I found that there are four hoses coming out of the tank.

1. Thick rubber, on top for filling up fuel
2. Thin rubber, on top for venting
3. Thin copper, below to the engine compartment (guessing this is the fuel intake for engine
4. Thin copper, on top. ?????

The fourth one I don't understand what it is. It is also going to the engine compartment but it is attached to the tank on top so it must be some kind of return?

If anyone knows, I would appreciate the help! Thank you.

[zeehag]

diesels use a return also to tank from engine.
tank filler
tank vent
to engine
return from engine
4 hoses.

[Captain Bill]

diesel fuel pumps tend to pump more than the engine needs. Excess is returned to the tank.

[hd002e]

Thank you for your help.