This small valve is the charcoal canister solenoid. It is used to purge fuel tank vapors into the inlet manifold above 2000rpm I think. You should live it connected with the manifold and just put a bolt or something with a hose clamp to plug the pipe that was connected to the engine breather. If you like to remove the big hose with the "T" and connect the small hose from the carbon canister line directly to the manifold you should leave the non return valve on the manifold in place otherwise the boost will inflate your fuel tank!