2003 2.3L ..... my evap canister vents to atmosphere through a box called the fuel vapor separator. I have mine out and its super light with no rattles, and air blows easily both directions without resistance and with no crud or particles coming out. Does that sound normal? And what's this thing supposed to do? Last carbon charcoal line of defense to catch fuel vapors before the atmosphere, or something else?

 

EVAP system's Vent valve is opened after engine has been off for awhile

i.e. when you stop for gas, you unscrew the gas cap you should here a "whoosh" of air being sucked into the tank because EVAP system put some negative pressure in the gas tank to suck out air inside, through the charcoal filter, and into the intake so the extra gas fumes, from the gas sloshing around while driving, won't pollute the air

After engine is off this negative pressure will eventually go away, there is a pressure sensor on the gas tank, computer will then open EVAP vent that allows air from inside the gas tank to vent out, but thru the charcoal filter
This allows for pressure equalization if its a warm day and gas in the tank heats up a bit and expands

Easy to follow diagram here: https://www.aa1car.com/library/evapobd2.gif

HOW the EVAP system works is car maker and year specific, i.e. the software it uses to open and close valves and the pressure levels used to trigger these

So yes, if vent is out of the truck it should be open, or if key has been off for a few minutes it should be ofpen, or if you remove gas cap and pressure drops to 0 it should be open after that