Cadillac Repair: 93 Deville 4.9 300c.i., fuel pressure gauge, schrader valve

Question
I need to change the fuel filter, but am confused on the procedure on how to relieve the fuel pressure before disconnecting the fuel lines.
There looks to be a fitting under a plastic covering on top of the front valve cover by the PCV valve. I believe this is the valve used to measure the fuel pressure. Can I simply turn this silver fitting to relieve any pressure? Do not have a fuel pressure gauge. If the engine has not been started for the day and is stone cold could I simply unscrew this fitting with a shop rag, and let the gas flow??
Thanks
William

Answer
Under that fitting is a schrader valve just like you have when you put air in your tires. With a COLD engine, You can wrap a towel around this schrader valve an SLOWLY depress it and the fuel will leak out onto the towel.

BE CAREFUL NOT TO GET IT INTO YOUR EYES.