That's the F shaped thing in the back on top of my engine with a hose connected right? How do I pull it out to replace it and how do I know if it's bad.

 

If its "plugged" into one of your valve covers than yes.

I think you just pull up on it (should be a rubber grommet on the valve cover (you might post a pic to verify)

Usually the rattle test will give you some idea (take off the hose/valve cover and shake it to see if it rattles. Rattle=good, no Rattle=bad). I think they are only a couple bucks to replace for piece of mind anyways.

 

Sometimes a new one isn't needed. .... just shoot carb cleaner or brake cleaner and drain out the gunk to restore the rattle.

 

The F shaped piece is a fitting (one of the nipples may/may not be capped off) that fits onto the smog valve. The valve hand presses into the rubber grommet inserted into the valve cover.

Shake the valve, it's it good, it will rattle. If it's gummed up, it won't. Clean it if it's gummed up, as it usually doesn't need to be replaced.