See Figures 1 and 2
The EVAP control system prevents gasoline vapors from escaping into the atmosphere. When fuel evaporates from the fuel tank, the vapors pass through vent hoses or tubes to the carbon-filled EVAP canister. They are temporarily held in the canister until they can be drawn into the intake manifold when the engine is running.
The vapors are drawn into the engine at idle as well as when the engine is operating above idle speed. This system is called a Bi-Level Purge System where there is a dual source of vacuum to remove the vapor from the EVAP canister.
The hoses used in this system are specifically manufactured. If replacement becomes necessary, it is important to use only fuel resistant hose.