95 astro wont p smog test due to...?

gas test i guess its a new test for older cars and they told it couldnt p cuz theres a tube running from the gas take to the front of the van and it ends up in a "gas canister" but the "fuel tank line" aint there so i was wondering if anybody knows how to find the line? i need this gas vapor tube to p the gas test plz thank you!!!