Evaporative fuel system

[cigar-]

I have a 1971 C10 that I am working on. In the process I noticed a black plastic cannister mounted on the core support passenger side. Someonetold me this the "evaporative fuel module". After a bit of noodling around I see there are connections to the fuel system.

Right now only one inlet on top has something connected to the cannister. The other two fitting have a remnant of fule line hose attached. Does anyone know how this system works? Is it necessary to have all of the fittings connected?

My truck is a California vehcle and is outside of the smog requirements. When I bought it the truck ran ok. Now that I am putting in a new motor and fixing other problems, I'd like to know if I can leave this thing disconnected. Also....does the other two fittings being open to the atmosphere adversely affect the truck's performance.

Thanks in adavnce for any and all help.

Michael