What causes purge valve to leak gas

Hello, That means the vapor canister is completely full, and the fuel has nowhere to go except in the engine. This system is designed for vapor, not fuel, so it needs to dry out. When you get gas, don't give it the extra few squeezes in there. When it clicks off, it's done. I would check the condition of the purge valve at this point. Since fuel can get out, air can get in, so at least it needs to be resealed.