Do these really need to be purged? Since I'm planning to use this on the vent line of the tank, air will come in thru the canister as well as trap fumes while the car is not running. This line will just have a air cleaner of its own attached to it....lawn mower type. The other line will go to the tank. Maybe I should use 2 vents on the tank. One would be used as described, the other would be a one way such as a check valve on a power brake unit. The check valve line would provide extra flow during high fuel useage..ie full throttle. Under normal cruise the air coming into the tank would come in thru the canister. If it needs a little more, the air can come in thru the check valve. All venting going out of the tank however will go thru the canister. The check valve could also be an inverted tip over valve,..ball bearing type.
This isn't an emmission application except to prevent fumes from entering the car.