Since I have a couple petcocks on my workbench, I went out and gave it a shot. Mine are off a 78, so they could be different from yours. These are a two piece filter, the bottom about 1 1/2 inches high the top about 1 inch. The top pulls off easily, the bottom, not so much. After prying the sides with a small screwdriver, I was able to work it up out of the hole a small amount. I couldn't really grasp the sides without wrecking the screen and the tube inside. I took a small vise grip to the pickup tube, and wiggled it back and forth till it came out, then I could pry the filter out of the hole with a small chisel and a little pliers action.
Good luck,
Philip