Gas Cap for '70 Nova

[m22mike]

Don't drill your vented caps... ...I am quit sure they are designed to allow some positive pressure in the tank, it helps the crappy little fuel pump work better.
When I have been driving Black Beauty... ...and pull in for gaz, I always crack the cap for a few seconds to allow the tank to vent off. Never tried it after the car has set all night.
If you and try blowing through the hole on the back of a vented cap you will notice it requires a small amout of effort before you get any flow.
The vented cap also has a negative pressure relief built into it as well. You can check this function by sucking on that little round thing in the back of the cap..
For you guys that are not in touch with your masculine side or are
affraid of germs, use a Mighty Vac...