Powerhead tubes '78 Merc 900

[MXHowes]

I'm doing a little maintenance on my '78 900. There are two tubes which go from the top of the powerhead down and out of sight. the larger one ~1/4" is the visual water circulation tube. The smaller one ~1/8" which starts close to the flywheel and goes out of sight behind the fuel pump is what? I'm curious because the line is cracked with age and I will replace it but what does it do?
Thanks, Jim

[boats.net]

They are recirculating hoses. Keeps fuel and oil from puddling on any one cylinder.