Fuel tank venting??
OK so what is different in the car from factory? Have you removed the "carbon can" evap control system? That WAS the vent originally.
You MUST be careful to get "whatever is there" (or whatever you build) ABOVE the fuel so it will not siphon. Originally, there was a 1/4" tube coming from tank up to engine bay beside the main fuel tube. That IS (was) the vent, and originally had an anti-spill valve in the end of that tube.
We need to know what you are changing