In a post dated 12/13/09, Mavaholic stated: "You can very easily make your nonvented cap into a vented cap. Look at the back and you will see a hole in the middle. In that hole is a check valve. It allows air into the tank, so it dont pull a vacuum as the gas is sucked out, but will not allow air out of the tank. All you have to do is take a drill the same size as the hole and drill out the check valve. Its plastic so very easy to do. You can verify it is now vented by blowing through it. Then you can plug up the vent line on top of the tank." This makes sense to me...I think. Has anyone tried this? I'm on a mission. Mike