Technical What is the hose for?

I have a 53 Merc Flatty and have this hole plugged in mine. In the pic attached here, there is a black hose coming off the intake towards the rear (between the rear carb and fuel pump). What is the hole/hose for? My builder plugged mine. Just curious. Does the hose run a vacuum to something?

 

Wipers.

 

It is a vacuum port, could be use wipers or anything that needs vacuum.

 

Ok thanks for the info.