I don't use a check valve, but I do use a filter. I also run the vent line to the top back of the tank then out the bottom front to create an "anti-siphon loop". Works well.

Also, I don't plug the vent line, especially if taking the plane from the 40 degree field into the 70 degree house... creates pressure in the tank and on the carb. Using the loop, I store the plane in the basment without any fume problems whatsoever.