Stock cap ready to be modded
Pry off the button in the off position
Once off it reveals the vent hole
Drill the hole larger to accept the hose barb
brass hose barb
installed into cap with JB Weld
Once JB Weld Drys, paint it with a quality paint.
Now all that is left is to put a hose on it. Drill a hole in the dash to stick the hose though, you want it pointing down. You can also run it to the top of your snorkel tube, or just put a few coils in the hose under the fender.