Hole in carburetor manifold

There is a hole in the side of the carb manifold on my kz250 with a hose sticking out of it, the owner before me obviously cut the hold in it and put it there. Does anyone know what this would be for? I'm still new to motorcycle engines but this doesn't seem right to me.

Do you have a vacuum petcock?
Steve

Yeah I think so

After doing some research I just realised what that is for. I didn't know there was a difference between petcocks