The PVC was always to the carb up front. The vent line wasn’t plumbed to the PVC unless the carb was changed out where the suggestion of using a “T” to be used to connect them was in the carbs instructions. I agree with capping the others IF there is a gas smell issue.
Cap the canisters open tubes. This way the other line(s) have vacuum on them and operate as normal. This should prevent a heavy gas smell.