Look at the hoses on the ones in the junk yard carefully. If the hose to the intake runs to the air filter then you would have to have some way of closing off the air filter housing until the engine starts. Otherwise the vapors just end up in the atmosphere anyway. On the older systems you'd have the hose from the gas tank to the canister. The other hose would go to a manifold vacuum source, for example the PCV hose, so the vapors were sucked into the engine when it was running. There's a ported vacuum controlled valve in the manifold vacuum hose that doesn't allow manifold vacuum to the canister unless you're off idle.