Bing 64 vent tube discoloration

I've  seen rubber fuel hose, polyurethane tubing and the yellow tygon tubing. They will all work when installed correctly.

Is it necessary to be able to see if any fuel is coming out of the carb drains?

"Is it necessary to be able to see if any fuel is coming out of the carb drains?"

I do not believe so.

If you lean towards obsessive behaviour (as I do) then you may feel compelled to know exactly what is happening, in relation to airbox, fuel pump & oil tank breather tube/drains. I currently have a catch can on the fuel related drains. My home made oil catch can was largely ineffective, so removed, pending a redesign.😈