My freiend has G20 GM Van with 305 motor and all parts were taken apart, every connectors are disconnected. one question I have is that "what is this small fitting between input and output. it look alike one of vacuum or vapors tube going.
does anyone tell me what that is and what can I does with.

Anyway you can post a picture for us?

Typically that'* an evap tube. It'* for excess pressure or vapor to be routed up to the engine for burning.